BackgroundFew studies have employed formal diagnostic criteria to determine the prevalence of psychiatric disorders in contemporaneous samples of children with and without intellectual disabilities.AimsTo establish the prevalence of psychiatric disorders against ICD—10 criteria among children with and without intellectual disabilities, the association with social/environmental risk factors, and risk attributable to intellectual disability.MethodSecondary analysis of the 1999 and 2004 Office for National Statistics surveys of the mental health of British children and adolescents with (n=641) and without (n = 17774) intellectual disability.ResultsPrevalence of psychiatric disorders was 36% among children with intellectual disability and 8% among children without (OR=6.5). Children with intellectual disabilities accounted for 14% of all British children with a diagnosable psychiatric disorder Increased prevalence was particularly marked for autistic-spectrum disorder (OR=33.4), hyperkinesis (OR=8.4) and conduct disorders (OR=5.7). Cumulative risk of exposure to social disadvantage was associated with increased prevalence.ConclusionsA significant proportion of the elevated risk for psychopathology among children with intellectual disability may be due to their increased rate of exposure to psychosocial disadvantage.