The objective of the Diabetes Prevention Program (DPP) is to prevent or delay the development of type 2 diabetes in those high-risk individuals who have tested positive for impaired glucose tolerance on an oral glucose tolerance test. The DPP is a multicenter randomized clinical trial in the U.S. with three intervention arms--lifestyle, metformin, and placebo--with 1,000 participants in each arm who will be recruited over a 3-year recruitment period and will be followed for 3 years after the study-wide closing date for recruitment, resulting in a 3- to 6-year participant follow-up interval. The primary outcome is the development of diabetes according to the revised American Diabetes Association criteria, confirmed with a repeat test. Recruitment ended in the spring of 1999. As of 14 October 1998, the DPP had screened 133,683 individuals, of whom 26,518 had an oral glucose tolerance test, resulting in 3,048 randomized participants (585 of who were former troglitazone arm participants). Of the randomized participants, approximately 45% belong to an ethnic minority group, 67% are women, and 10% are > or = 65 years old. In conclusion, recruitment of subjects for the DPP has been highly successful, particularly with respect to recruitment of minority participants.