Data from 1,575 cases and 1,974 controls enrolled in 6 previously conducted case-control studies of diet and breast cancer have been analysed with respect to alcohol intake. There appears to be an absence of any association between consumption of up to 40 g of alcohol per day and risk of breast cancer, and a highly statistically significant and consistent elevated risk of breast cancer for drinkers of 40 g or more of alcohol per day, for whom the relative risk, as compared with that of non-drinkers, is 1.69 (95% confidence interval 1.19 to 2.40). This association is not due to confounding by a number of diet-related factors, including total calories, fat, fibre and vitamin C.