Epidemiologic findings regarding the relation between alcohol consumption and risk of breast cancer have been inconsistent. We performed a meta-analysis (a quantitative review) of the available data. To evaluate whether there was a dose-response relation between alcohol consumption and risk of breast cancer, we fitted mathematical models to the pooled data. There was strong evidence to support a dose-response relation in both the case-control and follow-up epidemiologic data. Using the dose-response curves that we calculated, the risk of breast cancer at an alcohol intake of 24 g (1 oz) of absolute alcohol daily (about two drinks daily) relative to nondrinkers was 1.4 (95% confidence interval, 1.0 to 1.8) in the case-control data and was 1.7 (95% confidence interval, 1.4 to 2.2) in the follow-up data. We interpret these findings not as proof of causality, but as strongly supportive of an association between alcohol consumption and risk of breast cancer.