[The joint research project "Comorbidity and multimorbidity in primary care" (MultiCare)]. 
MultiCare is the acronym for a multidisciplinary and multicenter research network on multimorbidity and comorbidity in the primary care/family medicine setting, which is coordinated by the Institute of Primary Medical Care of the University Medical Center Hamburg-Eppendorf.  Multimorbidity is one of the most difficult problems in primary medical care as little is known about the interaction of several diseases in a person with regard to etiology and disease progress.  Also, guidelines for the treatment of multimorbid patients are largely lacking.  Therefore, the aims of the MultiCare network include: the identification of multimorbidity patterns in the elderly primary care population, analysis of incidence and prevalence and of interactions within clusters, the investigation of severity and consequences for patients, as well as trials to improve physician-patient interaction in the case of multimorbidity.  During the first funding period (2008-2010) the network consisted of two observational and two interventional studies.  Their results as of summer 2011 are presented in the following article.