We studied the incidence of insulin-dependent diabetes mellitus (IDDM) among children up to 15 years old of Caucasian and Mapuche origin, in the IX Region of Chile between 1980 and 1993. The Mapuche, or native Chileans, have their own culture, language an distinctive ethnic characteristics. Data were collected according to the methods recommended by the Diabetes Epidemiology Research International Group. We diagnosed IDDM in 47 children, 22 boys and 25 girls. The average annual incidence was 1.27/100,000 inhabitants (95% confidence intervals (C.I.) 0.83-1.71/100,000). The highest incidence along this period was during winter and spring. There was significant difference (P < 0.0016) in the IDDM incidence in Caucasians (1.58/100,000, 95% C.I. 1.11-2.04) compared with Mapuche (0.42/100,000, 95% C.I. 0-0.95). These results show that Mapuche children have less chance of developing diabetes.