Using the prospective Hungarian childhood diabetes register, a nationwide case-control study was carried out to investigate the possible role of various non-genetic factors as risk determinants for type 1 diabetes in childhood. A questionnaire (covering family characteristics, social status, fetal and perinatal events, breast-feeding habits, infectious diseases and stressful life events) was sent by mail to all incident diabetic children in 1990 (n = 163) and to two referent children (for each diabetic child), matched for age, sex and county. Diabetic children had a tendency to have mothers > 35 years of age (odds ratio (OR) = 3.52; 95% confidence intervals (CI) 0.74-16.79), a lower proportion of their mothers had higher education (OR = 1.69; 95% CI 0.95-3.0) and these children tended to move home more frequently (OR = 1.99; 95% CI 0.97-4.1). Although the duration of exclusive breast feeding was similar in both groups, the proportion of diabetic children who received no breast milk tended to be higher (OR = 1.76; 95% CI 0.91-3.4). A higher proportion of diabetic children reported non-specific infections (OR = 2.94; 95% CI 1.19-7.21) and the number of stressful life events was higher in diabetic children aged 10-14 years (OR = 3.9; 95% CI 1.14-13.27). As the risk determinants for childhood insulin-dependent diabetes mellitus identified in our low-risk population appear to be similar to those detected in the genetically different, high-risk Swedish population, our study strongly supports an etiological role for these non-genetic risk factors in IDDM.