Exhibit 8.1

Subsidiaries of ARCADIS NV

CONSOLIDATED COMPANIES

|Entity                                          |  | Jurisdiction   
|----------------------------------------------- |  | ---------------
|ARCADIS G & M, Inc.                             |  | Delaware       
|ARCADIS Nederland BV                            |  | The Netherlands
|ARCADIS Europe BV                               |  | The Netherlands
|ARCADIS USA BV                                  |  | The Netherlands
|ARCADIS Latin America BV                        |  | The Netherlands
|ARCADIS International BV                        |  | The Netherlands
|PRC Holding BV                                  |  | The Netherlands
|ARCADIS Geraghty & Miller International, Inc.   |  | Delaware       
|ARCADIS Communications Construction LLC         |  | Colorado       
|ARCADIS Corporate Services, Inc.                |  | Colorado       
|ARCADIS G&M of Michigan, LLC                    |  | Michigan       
|Reese, Macon and Associates, Inc.               |  | Florida        
|Finkbeiner, Pettis & Strout, Inc.               |  | Ohio           
|Lawson, Noble & Webb, Inc.                      |  | Florida        
|ARCADIS US Holdings, Inc.                       |  | Colorado       
|ARCADIS Capital, Inc.                           |  | Colorado       
|FPS Architects & Engineers, Limited             |  | Ohio           
|ARCADIS G&M of Michigan, LLC                    |  | Michigan       
|ARCADIS Regio BV                                |  | The Netherlands
|ARCADIS PlanRealisatie BV                       |  | The Netherlands
|ARCADIS Geo- en Vastgoedinformatie BV           |  | The Netherlands
|BV Boreon                                       |  | The Netherlands
|Onroerend Goed Balkenweg BV                     |  | The Netherlands
|ARCADIS Infra BV                                |  | The Netherlands
|ARCADIS Support BV                              |  | The Netherlands
|ARCADIS Euroconsult BV                          |  | The Netherlands
|ARCADIS Bouw en Vastgoed BV                     |  | The Netherlands
|ARCADIS FM Beheer B.V.                          |  | The Netherlands
|ARCADIS Enterprises B.V.                        |  | The Netherlands
|ARCADIS Ruimte en Milieu BV                     |  | The Netherlands
|LB&P Ecologisch Advies B.V.                     |  | The Netherlands
|ARCADIS Projecten BV                            |  | The Netherlands
|ARCADIS CZ Environmental Services s.r.o.        |  | Czech Republic 
|Micon Bedrijfsadviseurs Milieu BV               |  | The Netherlands
|Serasea BV                                      |  | The Netherlands
|Heidemij Realisatie 3 BV                        |  | The Netherlands
|Copijn Utrecht Holding BV                       |  | The Netherlands
|Heidemij Realisatie Deutschland GmbH            |  | Germany        
|Glastuinverplaatsing Leidsche Rijn BV           |  | The Netherlands
|Ontwikkelings Maatschappij Floris V CV          |  | The Netherlands
|Glastuinbouwgebied Het Grootslag BV             |  | The Netherlands
|Bio Science Park I BV                           |  | The Netherlands
|BV Venlo TPN                                    |  | The Netherlands
|ROW de Ruiter BV                                |  | The Netherlands
|Wocomm II BV                                    |  | The Netherlands
|Stationswijk BV                                 |  | The Netherlands
|Heidemij Realisatie II BV                       |  | The Netherlands
|Heidemij Realisatie I BV                        |  | The Netherlands
|Konijn Hoorn Machinebouw BV                     |  | The Netherlands
|Iberica S.A.                                    |  | Spain          
|Copijn Utrecht BV                               |  | The Netherlands
|Copijn Utrecht International Tree Services BV   |  | The Netherlands
|Copijn Utrecht Tuin en Landschapsarchitecten BV |  | The Netherlands
|Copijn Utrecht Eurobomen BV                     |  | The Netherlands
|Copijn Utrecht Boomchirurgen BVBA               |  | Belgium        
|Copijn Luxemburg SA                             |  | Luxembourg     

---



|KAFI BV                                                     |  | The Netherlands
|----------------------------------------------------------- |  | ---------------
|Mandaat BV                                                  |  | The Netherlands
|Civiele Invorderings- en Juridisch Advieskantoor BV         |  | The Netherlands
|Vastgoed Data BV                                            |  | The Netherlands
|KLM Aerocarto BV                                            |  | The Netherlands
|Involon BV                                                  |  | The Netherlands
|Ilis BV                                                     |  | The Netherlands
|KLM Aerocarto NV                                            |  | Suriname       
|KLM Aerocarto Belgium BVBA                                  |  | Belgium        
|V.O.F. SAT                                                  |  | The Netherlands
|ARCADIS BMB Management Consultants BV                       |  | The Netherlands
|GP Kenia BV                                                 |  | The Netherlands
|SORCA Management Consultants NV                             |  | Belgium        
|Ingenieursbureau Grabowsky & Poort International BV         |  | The Netherlands
|ARCADIS Caribbean NV                                        |  | Curacao        
|ARCADIS St. Maarten NV                                      |  | St. Marteen    
|ARCADIS Curaçao NV                                          |  | Curaçao        
|ARCADIS Bonaire NV                                          |  | Bonaire        
|Grabowsky&Poort Puerto Rico Inc.                            |  | Puerto Rico    
|ARCADIS AQUMEN Facility Management B.V                      |  | The Netherlands
|ARCADIS Deutschland GmbH                                    |  | Germany        
|ARCADIS Ekokonrem Sp.z.o.o.                                 |  | Poland         
|Grupo EP Ingenieria y Servicios Integrales S.A.             |  | Spain          
|ARCADIS Belgium NV                                          |  | Belgium        
|ARCADIS Holding France S.A.                                 |  | France         
|ARCADIS Consult GmbH                                        |  | Germany        
|ACD Vermessung GmbH                                         |  | Germany        
|ARCADIS Cert GmbH                                           |  | Germany        
|ARCADIS Bauconsult GmbH                                     |  | Germany        
|ARCADIS Ingenieure GmbH                                     |  | Germany        
|ARCADIS Liegenschaftsentwicklung GmbH                       |  | Germany        
|HOMOLA Projektmanagement AG                                 |  | Germany        
|ADM GmbH                                                    |  | Germany        
|HOMOLA AYH Project management B.V.                          |  | The Netherlands
|HOMOLA Projektmanagement s.r.o.                             |  | Czech Republic 
|HOMOLA AYH Holding GmbH                                     |  | Germany        
|EPTISA, Servicios de Ingenieria, S.A.                       |  | Spain          
|EP, Servicios Integrales de Gestions, S.A.                  |  | Spain          
|Auxiliar de Ingenieria, S.A.                                |  | Spain          
|ESRI Espana Geosistemas, S.A.                               |  | Spain          
|Sistemas de Informacion Territorial S.A. (Sitesa)           |  | Spain          
|EP Calidad, S.L.                                            |  | Spain          
|Alcalima Elenion, S.L.                                      |  | Spain          
|Casta Servicios Sociosanitarios, S.A.                       |  | Spain          
|Diseno, Desarrollo y Gestion de Centros de Visitantes, S.L. |  | Spain          
|Ibering Estudios y Proyectos, S.A.                          |  | Spain          
|Investigacion Tecnica y Calidad S.A.                        |  | Spain          
|Ingenieria del Atlantico, S.A.                              |  | Spain          
|Ingenieria de Instrumentacion y Control, S.A.               |  | Spain          
|Cinsa EP, S.A.                                              |  | Spain          
|NYE Sistemas, S.A.                                          |  | Spain          
|Electroconver EP, S.L.                                      |  | Spain          
|IHD, Handling España                                        |  | Spain          
|Eptisa Chile S.R.L.                                         |  | Chile          
|Eptisa Colombia S.R.L.                                      |  | Colombia       
|Eptisa Argentina S.A.                                       |  | Argentina      
|Eptisa Brasil S.R.L.                                        |  | Brazil         
|                                                            |  |                

2

---



|Casta Dano Cerebral, S.A.                           |  | Spain          
|--------------------------------------------------- |  | ---------------
|C.A. Santa Teresa de Arevalo, S.L.                  |  | Spain          
|C.A. San Juan de la Cruz, S.L.                      |  | Spain          
|Starke Diekstra NV                                  |  | Belgium        
|ARCADIS Gedas NV                                    |  | Belgium        
|ARCADIS Lapere NV                                   |  | Belgium        
|ARCADIS Fally NV                                    |  | Belgium        
|Domus Nitida NV                                     |  | Belgium        
|ARCADIS FCI S.A.S.                                  |  | France         
|Europe Etudes Gecti (EEG)                           |  | France         
|ARCADIS ESG                                         |  | France         
|Sobesol                                             |  | France         
|S.E.G.G.                                            |  | France         
|Geotechnika                                         |  | Czech Republic 
|Simecsol Consultants                                |  | Singapore      
|Mecasol                                             |  | France         
|Renardet S.A.                                       |  | Switzerland    
|Sauti Srl                                           |  | Italy          
|Renardet S.A. & Partners L.L.C.                     |  | Oman           
|ARCADIS GR                                          |  | France         
|Procedes Spaciaux de contruction (P.S.C.)           |  | France         
|Geolabo                                             |  | France         
|ARCADIS Chile S.A.                                  |  | Chile          
|ARCADIS Brasil Ltda                                 |  | Brazil         
|ARCADIS USHolding, Inc.                             |  | Delaware       
|ARCADIS Chile S.A.                                  |  | Chile          
|ARCADIS Brasil Ltda                                 |  | Brazil         
|ARCADIS Geotecnica S.A.                             |  | Chile          
|GC Consultores Geotecnicos                          |  | Peru           
|Geotecnica Consultores Ltd                          |  | Argentina      
|Arcadis Geotécnica Bouw Infra Ltda.                 |  | Chile          
|Consorcio Arcadis Geotecnica Mimetal Ltda.          |  | Chile          
|Inversiones de Infraestructura Cabo de Hornos Ltda. |  | Chile          
|ARCADIS Logos Engenharia S.A.                       |  | Brazil         
|ARCADIS Logos Energia S.A.                          |  | Brazil         
|Enerconsult S.A.                                    |  | Brazil         
|ARCADIS Hidro-Ambiente S.A.                         |  | Brazil         
|ARCADIS Tetraplan S.A.                              |  | Brazil         
|Damen Consultants BV                                |  | The Netherlands
|Partiform BV                                        |  | The Netherlands
|PRC Training BV                                     |  | The Netherlands
|PRC Bouwcentrum BV                                  |  | The Netherlands
|PRC Kostenmanagement BV                             |  | The Netherlands

3

---



NON-CONSOLIDATED COMPANIES

|Entity                                                |  | Jurisdiction   
|----------------------------------------------------- |  | ---------------
|Holland Environmental Venture Fund Commandite BV      |  | The Netherlands
|Holland Environmental Venture Fund Beheer BV          |  | The Netherlands
|Holland Environmental Venture Fund CV. Fund CV        |  | The Netherlands
|Stichting Fagoed                                      |  | The Netherlands
|Dynamicon BV                                          |  | The Netherlands
|EMDEME SA                                             |  | Portugal       
|Ecosystems BV                                         |  | The Netherlands
|Combinatie Oost-Achterhoek BV                         |  | The Netherlands
|Urbanet BV                                            |  | The Netherlands
|P.G.N. Parkeergroep Nederland BV                      |  | The Netherlands
|Brainliner BV                                         |  | The Netherlands
|Vermeer-Heidemij v.o.f.                               |  | The Netherlands
|Waterwolf Dienstverlening Buitenruimte BV             |  | The Netherlands
|Siberië CV                                            |  | The Netherlands
|Bio Science Park CV                                   |  | The Netherlands
|Grubbenvorst v.o.f.                                   |  | The Netherlands
|Combiflora v.o.f.                                     |  | The Netherlands
|VOF Meinga                                            |  | The Netherlands
|Eurotree GmbH                                         |  | Germany        
|Adviseurs Bouwplan Ontwikkeling BGN Partners BV       |  | The Netherlands
|Somerset                                              |  | Maryland       
|Sahelconsult Sarl, Ouagadougou                        |  | Burkina Faso   
|Afid Consultants Sarl                                 |  | Senegal        
|Euroconsult para Latinoamerica y el Caribe SA.        |  | El Salvador    
|Darwish Consulting Engineers                          |  | Egypt          
|Euroconsult Pakistan Ltd.                             |  | Pakistan       
|Brazilian Venture Consultants Ltda.                   |  | Brazil         
|Ilaco do Brazil Ltda.                                 |  | Brazil         
|Ilaco Suriname NV                                     |  | Suriname       
|Eurasia Consult Ltd                                   |  | Kazachstan     
|ARCADIS Konsult JSC                                   |  | Russia         
|Surgroma N.V.                                         |  | Suriname       
|CV Oude Grachtpad                                     |  | The Netherlands
|New Park, Planungs- und Entwicklungsgesellschaft GmbH |  | Germany        
|Umweltlabor GmbH                                      |  | Germany        
|Interplan Environmental Systems GmbH                  |  | Germany        
|Eurolabors AG                                         |  | Germany        
|Euro Facility Group Ltd.                              |  | United Kingdom 
|Jaakko Poyry Geotecnica Ltd                           |  | Chile          
|Proyectos Aeroportuarios Ltd                          |  | Chile          
|ORSA                                                  |  | Chile          
|Consorcio Reg. GC JRI Ing. Ltda                       |  | Chile          
|Consorcio Scetaroute-Grimaux, Varde, Geotécnica Ltda. |  | Chile          
|Consorcio Geotécnica JRI S.A.                         |  | Chile          
|Atlantis GmbH                                         |  | Germany        
|Multilatina Engineering Ltda                          |  | Brazil         
|Murta Energética S.A.                                 |  | Brazil         
|Biogás Energia Ambiental S.A.                         |  | Brazil         
|PIE-RP Termelétrica S.A.                              |  | Brazil         
|Cocal Termelétrica S.A.                               |  | Brazil         
|Cocal Termelétrica S.A.                               |  | Brazil         
|Breitener Energética S.A.                             |  | Brazil         
|V.O.F. Stationseiland                                 |  | The Netherlands
|V.O.F. De Ruijterkade                                 |  | The Netherlands
|V.O.F. X-Pact                                         |  | The Netherlands
|V.O.F. Modieslab                                      |  | The Netherlands
|Geodynamique et Structure                             |  | France         
|Getu                                                  |  | Tunisia        
|SEM Savoie Labo                                       |  | France         
|Eurometudes                                           |  | Romania        
|Procedes Spaciaux de contruction (P.S.C.)             |  | France         
|Geomechanika, s.r.o.                                  |  | Czech Republic 
|Solidex, a.s.                                         |  | Czech Republic 
|Kamex, s.r.o.                                         |  | Czech Republic 
|Geoprojekt, s.r.o.                                    |  | Czech Republic 
|Terratech, spol. S.r.o.                               |  | Czech Republic 
|Terratec, spol. S.r.o.                                |  | Czech Republic 
|Geoinzenyring, s.r.o.                                 |  | Czech Republic 
|ZPD d.d.                                              |  | Croatia        
|                                                      |  |                

4

---



|ARCADIS Grabowski Grabowska |  | Poland  
|--------------------------- |  | --------
|Innovated Tree Services LLC |  | Delaware

5

---



QuickLinks