Background: Few studies have employed formal diagnostic criteria to determine the prevalence of psychiatric disorders in contemporaneous samples of children with and without intellectual disabilities. Aims: To 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. Method: Secondary analysis of the 1999 and 2004 Office for National Statistics surveys ofthe mental health of British children and adolescents with (n=641) and without (n=17 774) intellectual disability. Results: Prevalence 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. Conclusions: A significant proportion ofthe elevated risk for psychopathology among children with intellectual disability may be due to their increased rate of exposure to psychosocial disadvantage.