Increasing breast cancer rates among young women (<40 years old) have been reported by the population-based cancer registries in Brazil. A case series study was carried out in Rio de Janeiro aiming to obtain epidemiological information allowing the generation of hypotheses to be further evaluated in analytical studies. One hundred and ten women 20-35 years old diagnosed with breast cancer were interviewed to determine the role environment plays in patients cased upon residential location. A comprehensive questionnaire including personal information (medical and lifestyle antecedents, reproductive history, family history of cancer, chemical and radiation exposure) was employed, and the obtained data were further compared with data provided by controls (women without cancer). An unconditional logistic regression was further employed to ascertain the respective odds ratios (OR) and their 95% confidence intervals (CI). Seventy-one percent of cancer cases were sporadic breast cancer, and familial aggregation (first degree relatives) was observed in just 3.5% (5.5% including second-degree relatives). Forty (51.3%) of the cancer cases were reported to have resided at a distance of less than 20 m from an electrical power transformer. Bivariate analysis revealed OR = 5.62 (95% CI 2.63-12) for residential use of pesticides during adulthood, OR = 2.15 (95% CI 1.22-3.77) for dental diagnostic x-rays, and OR= 1.53 (95% 0.77-3.04) for living nearby an electrical power transformer. Further multivariate analysis showed an adjusted OR = 3.5 (95% CI 1.11-11.0) for residential use of pesticides, and an adjusted OR = 2 (95% CI 1.24-3.23) for dental diagnostic x-rays during adulthood. The observed results highlight the importance of exploring the contribution of selected environmental agents possibly involved in breast carcinogenesis among young women.