In Canada, individuals experiencing problems related to their alcohol and drug use receive treatment and rehabilitative care through services provided primarily through the publicly funded health and social service system. During the past decade, however, an increasing number of Canadians have received treatment for substance abuse at facilities located in the United States, with most of the cost for this treatment borne by the various provincial health insurance plans. This paper provides a comprehensive analysis of the Ontario experience of treatment for substance abuse in the United States. First, the policy and planning context for the use of American treatment programs by Ontario residents and the rationale for recent changes to the reimbursement guidelines for such out-of-country treatment is reviewed. Secondly, the major trends in utilization of American programs over the past decade will be described and comparisons drawn to trends in the development of Ontario's own treatment system. This information has been used to help guide the development of treatment services in Ontario. In addition, the data serve as a baseline to measure the impact of various policy and program initiatives recently introduced in Ontario to reduce the utilization of treatment resources based in the United States.