This study uses the attention deficit/hyperactivity disorder (ADHD) symptom ratings of professional care workers to estimate the prevalence of ADHD symptoms among children in day treatment centres (N = 162) and residential treatment centres (N = 195) in Holland. Although further research is needed, the study supports the suggestion that such ratings can add to reliable diagnostic outcomes when assessing the behavioural symptoms of ADHD in children in the centres. It is estimated that nearly a fifth of the children in such centres exhibit the symptoms of ADHD in the judgement of professional care workers. Model testing using confirmatory factor analysis favours a dimensional behavioural model that comprises all the three constitutional symptom dimensions of ADHD (inattention, hyperactivity and impulsivity) instead of the two-factor model as used in the DSM-IV (inattention and hyperactivity/impulsivity). However, the differences of fit between both models were only small and the hyperactivity and impulsivity factors were highly correlated. This suggests that, in practice, a two-factor model can also be appropriate. The issue of whether a two-factor or a three-factor model is more appropriate thus remains unsolved in this study.