The aim of this study was to examine potential factors that modify blood cholesterol among children in countries in which dietary and lifestyle habits are becoming westernized. Population data on serum total and lipoprotein cholesterol, anthropometric indexes, and dietary intake were reviewed and compared for children aged 1-18 y from Japan, Spain, and the United States. The data show that total serum cholesterol in Japanese and Spanish children recently exceeded the 75th percentile for US children, primarily reflecting LDL cholesterol, although both LDL and HDL cholesterol contributed. Adiposity indexes do not explain the trends observed. Total and saturated fat intakes increased substantially in both Japan and Spain but in Japan are still lower than intakes in the United States. The Hegsted equation was used to relate differences in serum cholesterol to dietary fat intake. Changes in total serum cholesterol followed established dietary correlations among children in Spain, but not in Japan. Serum cholesterol in Japanese children was predicted to be 0.20-0.32 mmol/L lower than in US children; actual concentrations were considerably higher. These results suggest that a rapid westernization of children's blood cholesterol concentrations has occurred in Japan and Spain. Changes in fat intake predict changes in blood cholesterol in Spain, but not in Japan. Differences in genetic response to diet in certain populations, such as the Japanese, may explain higher blood cholesterol concentrations with lower fat intakes compared with the United States.