The Republic of Ireland is considered a region of low type 1 diabetes incidence compared with the British Isles and the rest of Europe. To establish a baseline national incidence of type 1 diabetes, in those under 15 years, with a measure of case ascertainment. Prospective active monthly reporting of incident cases by paediatricians was undertaken, with survey of adult physicians, endocrinologists and nurse specialists nationally. A secondary source of case ascertainment was employed. The crude incidence rate of type 1 diabetes was 16.6 per 100,000 per year and the directly standardised incidence rate was 16.3 per 100,000 per year. The Republic has a high incidence of type 1 diabetes. Services should be planned and resources allocated accordingly. A register should be established to monitor changes in this important disease. Further study is required to explore differing incidence in Northern and Southern Ireland.