The objective was to evaluate the association between alcohol consumption and risk of breast cancer. Data from 38 epidemiologic studies on alcohol consumption in relation to risk of breast cancer in women were included in a meta-analysis. A qualitative literature review also was conducted. The results showed strong evidence of a dose-response relation; however, the slope of the dose-response curve was quite modest. For example, daily consumption of one alcoholic drink was associated with an 11 percent increase (95 percent confidence interval, seven to 16 percent) in the risk of breast cancer compared with nondrinkers. An explanation for the marked variation in results across studies was not found. The modest size of the association and variation in results across studies leave the causal role of alcohol in question. The evidence that alcohol consumption affects the risk of breast cancer, however, appears to be growing stronger.