In order to thoroughly analyze risk factors of breast cancer (BC) in premenopausal Uruguayan women, acase-control study was carried out at the Pereira Rossell Women’s Hospital, Montevideo, where 253 incident BCcases and 497 frequency-matched healthy controls were interviewed on menstrual and reproductive story, wereadministered a short food frequency questionnaire and undertook a series of body measurements necessary tocalculate body composition and somatotype. Odds ratio (OR) coefficients were taken as estimates of relative riskderived from unconditional logistic regression. Among the classical risk factors, only the family history of BC infirst degree relatives was significantly associated with risk of premenopausal BC (OR=2.20, 95% CI 1.33-3.62).Interestingly, this risk factor was found to be stronger in women of ages >40 (OR=4.05, 95% CI 2.10-7.81), latemenarche (OR= 2.39, 95% CI 1.18-4.85), early age for their first delivery (OR=3.02, 95% CI 1.26-7.22), shorttime between menarche and first delivery (OR=3.22, 95% CI 1.29-8.07), and with high parity (OR=4.10, 95%CI 1.79-9.36), although heterogeneity was detected only for age and parity. High consumption of red meat waspositively associated with the disease risk (OR=2.20, 95% CI 1.35-3.60), in the same way as fried foods (OR=1.79,95% CI 1.12-2.84). Conversely, a high intake of plant foods displayed a protective effect (OR=0.41, 95% CI0.26-0.65). Except for hypertension (OR=1.55, 95% CI 1.03-2.35), none of the analyzed components of metabolicsyndrome were associated to BC risk. Particular increases of risk for premenopausal BC were found for familyhistory in first degree relatives in certain subsets derived from the menstrual-reproductive history. Preventivestrategies could broaden their scope if new studies confirm the present results, in view of the limited preventionmeasures that premenopausal BC currently has.