Follow-up studies of diabetic patients, based upon the extensive experience of the Joslin Clinic of Boston from 1898 to 1961, demonstrate the great improvement in prognosis for persons with the disease. Gains have occurred at all ages but have been especially great in diabetics with onset in childhood. The 20-year survivorship rate among patients under age 15 1st seen between 1940-49 was nearly 85% and 75% for 15 to 29 year old patients. This improvement in longevity is due to advances in diabetes therapy and to the control of infections. Mortality from diabetic coma has been virtually eliminated, and that from diabetic gangrene has been sharply reduced. Nevertheless, mortality rates of diabetics exceed those of non-diabetics, the margin being proportionately greatest at ages under 35. Diabetics are prone to premature development of vascular lesions of all kinds. These conditions now account for more than 3/4 of all deaths. Widespread and severe lesions of the small vessels constitute a major problem in diabetes of long duration with onset in childhood or early adult life.