To examine the relation between alcohol consumption and breast cancer, the authors used data from the Centers for Disease Control's Cancer and Steroid Hormone Study, a multicenter population-based case-control study. Between August 1981 and December 1982, 3,498 US women aged 20-54 years with newly diagnosed breast cancer and 3,157 women aged 20-54 years selected at random from the same geographic areas were asked about their consumption of alcoholic beverages during the previous five years. Women who drank any alcohol had a risk of breast cancer of 1.0 (95% confidence interval 0.9-1.2) compared with nondrinkers. The risk of breast cancer did not increase appreciably with increasing alcohol consumption: Risk estimates for women consuming 8-14, 15-21, and 22 or more drinks per week were 1.1, 1.0, and 1.2, respectively. The authors also found no notable differences by type of beverage or within specific risk factor subgroups. These findings do not support the hypothesis that alcohol consumption increases the risk of breast cancer.