The metabolic control of 61 consecutive cases of adolescent diabetes was followed 1 year before and 1 year after the patients were referred from a pediatric to adult clinic. The level of control of the disease was determined by measurements of haemoglobin A1 made on visits to the out-patient clinic. No significant deterioration of the disease was noted on the first visit to the adult clinic. Boys and patients with a shorter disease history coped better with the transition period. During the first year of treatment at the adult clinic the metabolic control of the disease improved significantly (p less than 0.001). Girls and diabetics with a long disease history should be well-prepared for referral to adult clinics.