Benign breast disease (BBD) is common in women in the reproductive age group. The results of epidemiological studies that have examined the relationship between diet and BBD are controversial and scarce. The aim of the present study was to identify and evaluate the impact of dietary and reproductive risk factors in the development of BBD in Mexican women. Between 1994 and 1996, 121 women with BBD and 121 age-matched (+/- 3 yr) clinical controls with non-breast-related diseases were identified. The study population was directly interviewed about their reproductive history, and a semiquantitative food frequency questionnaire was used to obtain dietary information. The population was originally identified as part of a hospital-based case-control study examining exposure to 1,1-bis(p-chlorophenyl)-2,2,2-trichloroethane and breast cancer. A significant reduction in the risk of BBD was observed when comparing the upper with the lower tertiles of consumption of citrus fruit [odds ratio (OR) = 0.43, 95% confidence interval (CI) = 0.21-0.88], non-citrus fruit (OR = 0.35, 95% CI = 0.16-0.76), diary products (OR = 0.36, 95% CI = 0.18-0.75), and food sources of lignans (OR = 0.48, 95% CI = 0.24-0.98). A marginally significant reduction in the risk of BBD associated with the consumption of vitamin B-12 (OR = 0.48, 95% CI = 0.23-1.02) was also observed. Our results add new information about the role of diet in the etiology of BBD.