Background: The study of premature deaths in people with intellectual disability (ID) has become the focus of recent policy initiatives in England. This is the first UK population-based study to explore cause-specific mortality in adults with ID compared with the general population. Methods: Cause-specific standardised mortality ratios (SMRs) and exact 95% confidence intervals were calculated by age and sex for adults with moderate to profound ID living in the unitary authorities of Leicester, Leicestershire and Rutland, UK, between 1993 and 2006. Causes of death were also studied to determine how often ID and associated conditions, such as Down syndrome, were mentioned. Results: A total of 503 (17% of population) adults with ID died during the 14-year study period (30 144 person-years). Relatively high cause-specific mortality was seen for deaths caused by congenital abnormalities (SMR = 8560), diseases of the nervous system and sense organs (SMR = 1630), mental disorders (other than dementia) (SMR = 1141) and bronchopneumonia (SMR = 647). Excess deaths were also seen for diseases of the genitourinary system or digestive system, cerebrovascular disease, other respiratory infections, dementia (in men only), other circulatory system diseases (in women only) and accidental deaths (in women only). Two-fifths (n = 204; 41%) of deaths recorded in adults with ID mentioned ID or an associated condition as a contributing cause of death. Conclusions: Strategies to reduce inequalities in people with ID need to focus on decreasing mortality from potentially preventable causes, such as respiratory infections, circulatory system diseases and accidental deaths. The lack of mention of ID on death certificates highlights the importance of effective record linkage and ID reporting in health and social care settings to facilitate the government's confidential inquiry into causes of death in this population.