The objective of the present study was to investigate potential differences at presentation of type I diabetes and during its long-term clinical course in children and adolescents with prepubertal and pubertal manifestation. Clinical, immunological and biochemical characteristics at diabetes onset of 453 patients (320 prepubertal, 133 pubertal; median age at manifestation 7.1 years (0.7–13.9) and 13.1 years (9.2–17.6), respectively) were evaluated. Glycaemic control and exogenous insulin requirements were followed prospectively, with a median follow up of 9.4 years. At the onset of the disease no differences concerning the degree of metabolic decompensation, impairment of somatic health, and islet cell antibody status could be detected between the groups, except for a smaller body weight loss in pubertal patients (P=0.011). The duration of partial remission (insulin requirements <0.5 IU/kg body weight/day) was unrelated to age or pubertal status at onset. It was found to be longer in boys than in girls in the total cohort (median duration: 279 vs 215 days, P=0.0071). Despite an absence of differences during the early course of the disease, glycaemic control was better, and daily insulin doses were significantly lower in patients with pubertal onset, after 6 years of diabetes.