Prospective registry of newly diagnosed cases of insulin-dependent diabetes mellitus in subjects under 20 years began in 1988 in Aquitaine, Lorraine, Basse- and Haute-Normandie (population base = 2,288,018 inhabitants under 20). The registry gave a complete coverage of the population as the capture-recapture method gave a 98% yield. The mean annual incidence was 7.6/100,000 for the period 1988-1990. A specific survey aimed at describing clinical and biological presentation at diagnosis. The main symptom was polyuria in 98% of the cases, fatigue in 58% and weight loss in 44%. Abdominal pain was reported in 34% of the cases. Diagnosis was ascertained by measurement of plasma glucose, which was > or = 11 mmol/l in 95% of the cases and associated with ketonuria in 84% of the children. Coma in 13% of the children and acidosis (total CO2 < or = 18 mmol/l) in 48% showed the severity at diagnosis. Ketonuria and acidosis were significantly more frequent in the younger age group (0-4 yr). Diagnosis was made by a general practitioner in the majority of the cases; conversely insulinotherapy was initiated at the hospital in 95% of the cases. Initial insulin treatment was 2 daily injections. Following the French experience the collaborative network EURODIAB ACE has undertaken the same survey among the European Registries. Important geographical variations in incidence rates of IDDM in children has been reported across Europe but it is not known whether this interferes with presentation at diagnosis of the disease.