A survey was conducted in 1984-85, within Leicester City boundaries, which contains 64,535 children below the age of 15 years (20,267 Asian and 44,268 White Caucasian) to ascertain the prevalence of insulin-dependent diabetes mellitus (IDDM) using a central register maintained for the changeover to U-100 insulin, diabetic health visitor index cards, hospital admissions of diabetic children, and individual registers maintained by us. Overall prevalence per thousand for children aged 0-15 years was 0.54 for Asian and 0.99 for White Caucasians; for ages 10-15 years they were 0.97 and 1.87, and for ages 0-9 years, 0.31 and 0.38, respectively. This was not statistically different at the 5% level. Ours is the first population based study of its kind in Asian children, and challenges the view that there is a large difference in the prevalence of IDDM between Asians and White Caucasians. A wider analysis of this observation incorporating a large population base is suggested.