Objective: To investigate the effect of type 1 diabetes on pubertal onset and development, and to identify factors potentially affecting puberty, including glycemic control, relative diabetes duration, body mass index standard delta score (BMI SDS), insulin dose, and intensity of insulin therapy. Research design and methods: Initiated in 1990, the Diabetes-Patienten-Verlaufsdaten (DPV) is an ongoing, prospective longitudinal follow-up program to benchmark the quality of diabetes care provided to, predominantly, pediatric patients. Data collection for this non-interventional audit was carried out at 202 German diabetes treatment centers. Patient recruitment was done by referral, clinic/hospital ascertainment, or self-report. Data were analyzed for subcohorts of 1218-2409 boys and 579-2640 girls from a cohort of 24 385 pediatric type 1 diabetic patients. Selection was based on ethnicity and availability of data on Tanner stage 2, or higher, of genital and pubic hair development (boys) or breast and pubic hair development, and menarche (girls). Results: Boys showed significant (P!0.05) delay (years) in mean ages at onset of genital development (12.0 (G0.9) years) and pubarche (12.2 (G0.4) years). In girls, mean ages at thelarche (11.4 (G0.5) years), pubarche (11.5 (G0.1) years), and menarche (13.2 (G0.5) years) were significantly delayed compared with the general population. Sexual maturity (Tanner stage 5) was not delayed in either sex. Elevated glycohemoglobin and decreased BMI SDS were associated with significantly delayed pubertal onset, whereas relative diabetes duration and insulin dose were not. Conclusions: Pubertal onset, but not sexual maturity, is delayed in children with type 1 diabetes. Delay increases with higher glycohemoglobin and lower BMI SDS.European Journal of Endocrinology 157 647-653