Background Prevalence of intellectual disabilities varies considerably between studies. People with intellectual disabilities experience health inequalities, but most studies comprise small or incomplete populations. We investigated in a whole country population the (1) prevalence of intellectual disabilities and (2) general health status compared with the general population.

Method Data were from Scotland’s Census, 2011. We calculated the prevalence of intellectual disabilities, reported general health status of people with and without intellectual disabilities and the extent of health-related limitations to daily activities. We conducted logistic regressions to determine the ORs of intellectual disabilities predicting poor health and associations with age and gender.

Results Of Scotland’s 5 295 403 population, 26 349 (0.5%) had intellectual disabilities; 15 149 (57.5%) were males and 11 200 (42.5%) were females; 5234 (0.6%) were children/youth (0–15) and 21 115 (0.5%) were adults (16–75+ years). Identification of intellectual disabilities rises until age 5 years, with a further small rise by age 9 years. Children and adults with intellectual disabilities reported more poor health (47.9% and 40.3%) than the general population (2.1% and 13.8%) and were more limited in activities by their health. Intellectual disabilities had an OR of 43.2 (95% CI 40.8 to 45.7) in predicting poor health; the influence of increasing age on poor health was markedly interacted by presence of intellectual disabilities, likely to be due to a ‘healthy survivor’ effect within the intellectual disabilities population.

Conclusion People with intellectual disabilities have poorer general health than other people, especially children and young people. Accurate information on population prevalence and health status is essential to plan appropriate resources.