An important final step in the life cycles of programs and their evaluation involves assessing new programs' or innovations' sustainability. This review and synthesis of 19 empirical studies of the sustainability of American and Canadian health-related programs examines the extent of sustainability achieved and summarizes factors contributing to greater sustainability. Three definitions for measuring sustainability were examined: continued program activities (18 studies), continued measured benefits or outcomes for new clients (2 studies), and maintained community capacity (6 studies). Methods of studying sustainability were also assessed. In 14 of 17 studies covering the continuation of program activities, at least 60% of sites reported sustaining at least one program component. Although these studies' methods had substantial limitations, cross-study analysis showed consistent support for five important factors influencing the extent of sustainability: (a) A program can be modified over time, (b) a "champion" is present, (c) a program "fits" with its organization's mission and procedures, (d) benefits to staff members and/or clients are readily perceived, and (e) stakeholders in other organizations provide support.