In order to study the importance of out-patients' supervision on survival, a prospective study of 1061 juvenile diabetics was performed. After the first hospitalization at the Steno Memorial Hospital 5.3 +/- 4.5 years after the onset of diabetes, this population of diabetics was divided into two comparable groups by their own practitioners. One group (n = 525) was referred for further out-patient supervision to the out-patient clinic, the other group (n = 536) was not. 96.7% of the patients were followed at least 25 years. A highly significant increased survival was seen in patients seen in 4-5 times a year at the diabetic out-patient clinic. Death from ketoacidosis, hypoglycemia, and suicide was significantly higher in the group not referred for further out-patient control, and death in uremia occured earlier in this group. Juvenile diabetics with long-standing diabetes and persisting endogenous insulin secretion evaluated on the basis of C-peptide examination had significantly less severe retinopathy and nephropathy than comparable patients without endogenous insulin secretion, and survival of juvenile diabetics with clinical indications of persisting endogenous insulin secretion seems not to be different from non-diabetics.