The prevalence of Type 1 diabetes in Malta was estimated by identifying all cases aged less than 32 years by the end of 1987 who had attended the island's principal diabetic clinic. The age-adjusted prevalence rate for 0-19 year olds was 110.3 per 100,000 (girls 126.2 (n = 65), boys 95.3 (n = 52]. The mean annual incidence, during the period 1980-1987, in 0-19 year olds was 13.3 per 100,000 (n = 113, girls 14.1 and boys 12.6). Males developed Type 1 diabetes 2.1 years later than females (13.7 +/- 6.9 (+/- SD) vs 11.6 +/- 6.7 years). The commonest age of onset was 10 to 14 years. The peak period of onset occurred during the cooler months of November to February. The incidence rates are close to those in Nordic countries and indicate that Type 1 diabetes in Malta is underestimated.