Studies of adult diet and risk of breast cancer have yielded mainly null results, but this does not rule out a possible impact of adolescent diet. This study examined associations between components of adolescent diet and risk of proliferative benign breast disease (BBD), a marker for breast cancer. The study population consisted of 29494 women in the Nurses' Health Study II who completed a questionnaire on adolescent diet in 1998 and who were 33-53 years of age at that time. A total of 470 new cases of proliferative BBD were identified between 1991 and 1997. Incidence rate ratios (RRs) and 95% confidence intervals (CIs) were calculated for quartiles of energy-adjusted intakes, using the lowest quartile of each as the reference group. Total fat intake during adolescence was unrelated to risk of proliferative BBD, although there were positive associations for intakes of animal fat and monounsaturated fat and an inverse association for intake of vegetable fat. For vitamin E intake, the multivariate RRs were 1.13, 0.88, and 0.79 (95% CI, 0.61-1.04) for women in the second, third, and highest quartiles, respectively (P for trend = 0.05). The multivariate RRs were 0.94, 0.99, and 0.75 (95% CI, 0.57-0.98) for women in increasing quartiles of fiber intake (P for trend = 0.05). Vegetable fat, vitamin E, and fiber intakes during adolescence were inversely associated with risk of proliferative BBD in this population. Confirmation of these associations may suggest a means for prevention of breast cancer.