Background: It has been suggested that persons with an intellectual disability consume a disproportionate amount of hospital services. Policy changes in Ontario in the 1970s and 1980s made it necessary for community health services to accommodate this population that formerly received most of its medical care in the institutions where they lived. It is frequently suggested that community health services are currently inadequate to care for this population. Methods: The study was a retrospective analysis of routinely collected hospitalization data for persons living in Ontario with an intellectual disability, between 1995 and 2001. Results: A substantial proportion of hospitalizations of persons with an intellectual disability were for mental disorders and dental diseases. Of all in-hospital stays, one-third were for mental disorders such as schizophrenia and depression. Of all day-surgery admissions, almost 40% were for dental diseases corresponding to a high rate of dental procedures. The study also identified high ambulatory care-sensitive condition hospitalization rates. In-hospital surgical procedure rates, however, were low. Interpretation: This study is the first to fully describe patterns of hospitalization for persons with an intellectual disability in Ontario, Canada. A recurring finding is the large discrepancy between statistics for persons with an intellectual disability and published data for the general population. The study limitations mean further research is required to confirm the results and to determine if persons with an intellectual disability are receiving the health care they are entitled to in Ontario.