Valid community-based data on the prevalence of chronic diseases in adolescents (12-18 years) with intellectual disability (ID-adolescents) are scarce. The aim of this study was to assess the prevalence rates and the nature of chronic diseases in a population of ID-adolescents and to compare them with the rates among adolescents in the general population. Therefore, we obtained data on 1083 ID-adolescents attending secondary schools, day care centers or living in residential centers fully covering one region of the Netherlands. Parents of the adolescents completed a questionnaire about the occurrence of chronic diseases in their child during the previous 12 months and about background characteristics. The questionnaire was derived from the Dutch National Permanent Survey on Living Conditions questionnaire periodically administered in a representative population sample (n [approximately equal to] 10,000). Prevalence rates of chronic diseases in ID-adolescents were compared with those in adolescents in the Dutch general population. Among ID-adolescents, high prevalence rates of a wide range of chronic diseases were found. The five most prevalent were: ADHD (21.1%), PDD-NOS (14.0%), dyslexia (13.9%), migraine or chronic headache (12.7%), and autistic disorder (10.9%). These prevalence rates were all higher (p less than 0.05) than among adolescents in the general population. Of all ID-adolescents, 62.9% was reported to have at least one chronic disease. The burden of chronic diseases among ID-adolescents is very high, showing a high need for adequate care. These high prevalence rates should alert policymakers and clinicians regarding the widespread of chronic diseases among ID-adolescents. (Contains 3 tables.)