66 and psychologist (R′ 3.5) visits. IROS primarily provides information from medium to high health burden levels and factor scores ranged from 0.41 (lowest) to 0.967 (highest burden). A significant impact on health burden could only be proven for the ‘state at discharge’ (p= 0.015), although there was a tendency towards worse factor scores for children that were older, had a higher Injury Severity Score or after traffic injury. In conclusion, we showed that the burden of health problems for children and families after severe trauma is still high and physical, as well as psychosocial in nature. The health state at discharge seems to predict long-term outcome, which might be of impor- tance in view of, e.g. trajectory assistance. IROS may provide an improved scoring system to evaluate outcome after (paediatric) injury or critical illness. Keywords Trauma . Outcome . Child . International Classification of Functioning . Item Response Theory Abbreviations AIS Abbreviated Injury Scale CI Confidence interval e.g. Example given ICF-CY ICF (WHO), version for children and youngsters ICF International Classification of Functioning (WHO) i.e. it est IROS ICF-related outcome score IRT Item Response Theory ISS Injury Severity Score OR Odds ratio PENTA A paediatric network around trauma (Flanders, Belgium) POPC Paediatric overall performance category R′ Liddell’s exact estimated relative risk SD Standard deviation y Years of age z01 Factor score, rescaled to [0,1] Background Important long-term health problems have been described in adults and children after critical illness or severe trauma. These problems are seen in all dimensions of health and include among others emotional or intellectual functioning, but also locomotion, problems with sexuality, burden on caregivers [1, 18, 20, 26, 32]. Several authors therefore advise the systematic collection of outcome data in research and daily practice [2]. Still, studies describing long-term outcome of severely injured children are relatively sparse. Eur J Pediatr (2011) 170:65–73 Moreover, published data are not necessarily representative for the local situation, because of cultural or regional health system differences. Existing studies often suffer from selection bias due to exclusion criteria, drop-out or instrument-related issues [8, 25, 37]. Further, most instru- ments measure only certain domains of health [14, 21, 22]. The choice of these domains is rather arbitrary and often not related to a strong underlying construct. Instruments are thus under discussion because of shortcomings in their content validity and/or in the justification of the methods used, but also because of problems with certain assumptions made (e.g. equality of interval distance, independence of attributes) [6, 10, 14, 15, 33]. In addition, for most instruments, the evidence of validity in severely injured children is still limited [27, 36]. In 2001, the World Health Organisation endorsed the International Classification of Functioning (ICF) as a conceptual framework and a ‘common language’ to describe health [38]. As part of the Flemish Paediatric Trauma Registry (PENTA), we evaluated long-term outcome in children and their families after severe trauma by means of a questionnaire based on this ICF construct: the ICF-Related Outcome Score (IROS) [35]. The aim of this report is to describe that outcome and the characteristics of the IROS instrument in doing so. Methods Patients and controls Patients were recruited from the PENTA registry (Flanders Belgium, 2005) [35]. Review board approval and informed consent were obtained. All surviving children with ‘severe’ trauma, i.e. hospitalised >48 h were eligible (n= 229). Exclusion criteria included loss of follow-up (n = 15), language barrier (n =19) and child abuse (n= 4). Follow-up was planned after 12 months. A questionnaire was sent by post, supported by telephonic reminder (up to three times); the response rate was 76.4% (n = 146). The primary respondent was a parent or guardian. The control popula- tion (n = 265) consisted of children without recent ‘severe’ trauma or severe chronic disease, recruited from different groups: children from hospital personnel, a nursery and a secondary school. We used propensity score matching and created matched pairs (n =133) between the trauma and control groups to correct for observed imbalances in the covariate distributions (age and gender of child, marital status and education level of proxy; see Table 1) [30]. Further analysis was done only in these matched groups. For the trauma cases the median Injury Severity Score (ISS) was 9 (min 1; max 43). Thirty point eight percent had an ISS above 15; 21% were categorised as ‘polytrauma’