We evaluated whether moderate alcohol consumption is associated with increased risk of developing benign breast disease (BBD), a potential "precursor" or marker for breast cancer development. This study evaluated associations between reported alcohol consumption and BBD diagnosis among 75,826 women in the Nurses' Health Study II. Between 1989 and 1997, 16,035 women reported a first diagnosis of BBD (317/10,000 person-years), of which 2,999 diagnoses were confirmed by tissue biopsy (59/10,000 person-years). Of the pathology specimens reviewed, 532 were nonproliferative benign breast conditions, and 932 were proliferative conditions. Person-time models provided estimates of the rate ratio (RR) and 95% confidence interval (CI). Reported recent adult consumption of alcohol was not associated with increased BBD incidence. Compared with women who did not drink alcohol, the age- and body mass index (BMI)-adjusted RRs for any reported BBD were 0.98 (95% CI, 0.95-1.02) for those who consumed <5 g/day, 0.93 (95% CI, 0.89-0.98) for those who consumed 5-14.9 g/day, and 0.90 (95% CI, 0.83-0.98) for those who consumed >or=15 g/day. The adjusted RRs for biopsy confirmed BBD and any proliferative benign condition were similiar. However, reported alcohol consumption of >or=15 g/day between ages 18 and 22 years was associated with higher rates of biopsy-confirmed BBD (age- and body mass index-adjusted RR = 1.14; 95% CI, 1.00-1.30), nonproliferative BBD (RR = 1.46; 95% CI, 1.09-1.96), and any proliferative BBD (RR = 1.33; 95% CI, 1.05-1.69), but not atypical hyperplasia. In this study, recent alcohol consumption was associated with slightly lower rates of reported BBD. However, greater alcohol consumption earlier in life (ages 18-22 years) was associated with higher proliferative BBD rates, suggesting that timing of exposure may be relevant to disease incidence.