Associations studies were attempted between the type of feeding, duration, and time of starting of solid foods in infancy and the incidence of insulin-dependent diabetes mellitus (IDDM). The study subjects comprised 52 IDDM patients and 52 control subjects matched for sex, age, social status, country, geographical location and selected from pediatric departments of different hospitals in Tehran. Diabetic children (21 boys, 31 girls) were of the ages of 1.5 to 14 years. Information about the pattern of their feeding at the first two years of life were collected through questionnaires administered to the mothers. The questionnaire was designed to evaluate the duration of complete or partial breast-feeding and the age at which dietary products containing cow's milk were introduced into the diet. A large proportion of the diabetic children rather than the control children had been breast-fed, and the risk of IDDM among children who had not been breast-fed was below unity. No significant difference in the duration of breast-feeding was observed between diabetic and control group. Our data do not support the existence of a protective effect of breast-feeding on the risk of IDDM, nor do the data indicate that early exposure to cow's milk and dairy products has any influence on the development of IDDM.