Background: Physical inactivity and obesity are highly prevalent in every Canadian province and territory. Purpose: To estimate the economic costs of physical inactivity and obesity for the province of Ontario in 2009. Methods: A prevalence-based economic burden analysis was undertaken. The relative risks of diseases associated with physical inactivity and obesity were determined from a meta-analysis of existing prospective studies and applied to the health care costs of these diseases in Ontario. The prevalences of physical inactivity and obesity were obtained from the 2009 Canadian Community Health Survey (CCHS) for the province of Ontario. Estimates of the economic burden were derived from both direct and indirect expenditure categories. Direct medical costs included hospital care expenditures, drug expenditures, physician care expenditures, expenditures for care in other institutions, and additional direct health expenditures; whereas indirect costs included the value of years of life lost due to premature death and the value of days lost due to short-term and long-term disability. Results: The prevalences of physical inactivity (