Background There have been very few populationbased studies of the prevalence of psychiatric disorders among children and adolescents with and without intellectual disability (ID). Methods Secondary analysis of the Office for National Statistics survey of the Mental Health of Children and Adolescents in Great Britain was performed. This survey collected information on a multistage, stratified, random sample of children between and years of age across postcode sectors in England, Scotland and Wales. Results The prevalence of any diagnosed ICD- disorder, conduct disorder, anxiety disorder, hyperkinesis and pervasive developmental disorders were significantly greater among children with ID than among their non-ID peers. There were no statistically significant differences between children with and without ID with regard to the prevalence of depressive disorders, eating disorders or psychosis. Factors associated with an increased risk of psychopathology among children and adolescents with ID included age, gender, social deprivation, family composition, number of potentially stressful life events, the mental