Prospective observations over a ten-year period of 108 juvenile diabetics treated with unmeasured diet are reported. Description is given of the patient material, circumstances at diagnosis, and course of management. Hyperglycemia and glycosuria were common, and ketoacidosis occurred often. Total plasma lipidswere elevated. Chemical control was unsatisfactory according to current popular standards. Growth was less in those with onset before puberty, and the men were underweight. Infections may have been excessive. Adolescent emotional difficulties were exaggerated. Educational, athletic, and vocational achievements probably equaled the normal expectation. Pregnancies were only 55 per cent successful when fetuses were viable. The prevalence of degenerative complication was similar to that reported from restricted diet studies. No factors were found to account for vascular disease. It is surmised that the general course of the patients compared favorably to those reported to be following diets. It is also suggested that if diet control does have favorable effects, then those reported to follow diets are not following them, or factors other than control are more influential on the progression of juvenile diabetic vascular disease.