The University Group Diabetes Program is a long-term prospective clinical trial designed to evaluate the effects of various hypoglycemic agents on vascular complications in patients with asymptomatic adult-onset diabetes. Mortality and blood glucose levels were determined as well as certain nonfatal events for patients assigned to diet alone or to either of two insulin treatment regimens. Lower levels of blood glucose with mean values close to normoglycemia were achieved in the treatment group in which the insulin dosage was adjusted to achieve normoglycemia compared with the levels achieved in patients treated with diet alone or with a fixed dose of insulin. In spite of differences in blood glucose levels among the treatment groups, there were only minor differences in the occurrence of fatal or nonfatal events.