The relation between alcoholic beverage consumption and risk of breast cancer was examined. We used data from a population-based, case-control study that included almost all incident cases occurring in five Spanish regions from February 1990 to July 1991. A total of 762 women between 18 and 75 years of age, with a histologically confirmed, first diagnosis of breast cancer, were compared with 988 control women. Alcoholic beverage intake was measured by an interviewer-administered, semiquantitative food-frequency questionnaire. We used 'nondrinkers' as the reference category and divided the remainder into four categories according to alcohol intake. The multiple logistic analyses included not only alcohol intake but also possible confounding factors such as total caloric intake, age, socioeconomic status, and reproductive and medical histories. Even at moderate levels of alcohol intake (less than 8 g/day), a 50 percent increase in risk of breast cancer was found. The trend across categories of intake was statistically significant for wine and distilled drinks, as well as total alcohol intake. Consumption of 20 g or more of alcohol per day was associated with a 70 percent elevation in breast cancer risk compared with that of nondrinkers (adjusted relative risk (RR) = 1.7, 95 percent confidence interval = 1.3-2.3). Although the magnitude of the RR observed in our study was modest, our findings provide further support for a positive association between alcohol consumption and risk of breast cancer.