BACKGROUND: The reasons behind the reported increase in the occurrence of childhood atopic sensitization rates are unclear. We wanted to evaluate the association between dietary fats, serum fatty acids, and the occurrence and development of atopic diseases. METHODS: From a longitudinal database of a population-based sample, 231 sex- and age-matched pairs in 1980 and 154 pairs in 1986 were chosen, between whom we compared the dietary data, serum fatty acid composition, and occurrence of atopic diseases. The same variables were also compared between those who developed atopic disease later and those who did not during the 9-year follow-up. RESULTS: Examination of the dietary data in 1980 for those who had developed atopic disease compared with those who had remained healthy showed that the atopic children had used less butter before the expression of atopy. According to the cross-sectional data, the children with atopic disease consumed more margarine (mean 8.6 vs 7.3 [P = 0.04]), and less butter (mean 9.4 vs 11.6 g/1000 kcal [P = 0.002]), than the nonatopic children in 1980. Differences supporting these dietary findings were similarly found in the serum fatty acid data. CONCLUSION: The diet of the atopic children differed from that of the nonatopic children in the consumption of polyunsaturated fat.