Caffeine consumption was significantly associated with serum cholesterol levels in women but not in men in a cross-sectional study of 4757 Australians. Use of caffeinated coffee by men, but not total caffeine consumption rate, was significantly associated with raised serum cholesterol. Potential confounding factors including age, adiposity and occupation were controlled for in this analysis. After adjusting for age and adiposity, the mean serum cholesterol level was 11 mg/dl higher for women consuming 200 mg or more of caffeine per day compared with those consuming less. The relative risk of high serum cholesterol (greater than 260 mg/dl) was greater than 2 for women consuming 200 mg or more of caffeine per day. A significant positive interaction between smoking and caffeine consumption in their association with serum cholesterol levels was found for females.