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Objective: To examine the relation between breast cancer risk and job history among women 20–44 years of age who participated in a multi-center, population-based, case–control study. Methods: Participants consisted of women newly diagnosed with breast cancer (1642) and controls identified by random-digit dialing (1494). Details about the three longest jobs were collected and coded by an industrial hygienist. Odds ratios and 95% confidence intervals were calculated and adjusted for age, study site, and other breast cancer risk factors. Results: Several occupational and industrial categories were found to influence breast cancer risk. Stratification of the study population by parity revealed differences in breast cancer risk between the two groups for several occupational categories, including teachers, librarians or counselors (increased risk only among parous women) and natural scientists and mathematicians (decreased risk only among nulliparous women). Conclusions: This is among the first population-based case–control studies to examine occupational history and breast cancer risk in young women, with the ability to consider a wide array of potential confounders, including reproductive characteristics. This study provides further evidence of an increased breast cancer risk for several occupations and industries. Other findings were not as strongly supported by previous investigations.