Background. Intellectual disabilities (ID) are common and lifelong. People with ID have health inequalities compared with the general population, but little is known about the epidemiology of affective disorders in this population. This study was undertaken to determine the point prevalence of affective disorders, and to investigate factors associated with depression.

Method. This population-based study (n=1023) included comprehensive individual assessments with each person. A two-stage process was used for diagnosis of affective disorders. Factors independently associated with depression were investigated through logistic regression analysis.

Results. The point prevalence was higher than that reported previously for the general population; DC-LD yielded 3·8% for depression and 0·6% for mania. Additionally, 1·0% had bipolar disorder currently in remission, and 0·1% first episode of mania currently in remission. Similar to general population findings, depression was associated with female gender, smoking, number of preceding family physician appointments, and preceding life events. Important differences were the association of not having a hearing impairment, and the trends for not living in deprived areas, and being married. Unlike general population findings, not having daytime occupation and obesity were not independently associated; nor was previous long-stay hospital residence, severity of ID, or sensory impairments.

Conclusions. This study has found a high point prevalence of affective disorders in adults with ID. The factors associated with depression have differences to general population findings. An understanding of this is important in order to develop appropriate interventions, public strategy and policy, to reduce existing health inequalities.