Objective: This study aimed to determine occupational variations in the incidence of breast cancer in the population-based cohort of Nordic Occupational Cancer Study (NOCCA). Methods: The study included long-term follow-up data from almost 7.5 million Nordic women. Participants were assigned to one of the 54 occupational categories based on census records at the ages of 30–64 years. Sixty-two thousand cases of breast cancer were identified through record linkages between nationwide cancer registries in Finland, Sweden, Norway, Denmark, and Iceland, followed up between 1961 and 2005. Country-specific standardized incidence ratios (SIRs) with 95% confidence intervals were estimated. Results: Overall, the highest risk elevations were seen among military personnel (SIR 1.58, 95% CI 1.03–2.32), dentists (SIR 1.43, 95% CI 1.31–1.56), and physicians (SIR 1.35, 95% CI 1.26–1.46). The lowest risks were observed among gardeners (SIR 0.76, 95% CI 0.74–0.78), farmers (SIR 0.80, 95% CI 0.78–0.82), and woodworkers (SIR 0.75, 95% CI 0.70–0.81). Welders, tobacco workers, and painters had higher SIRs for breast cancer diagnosed at age < 50. A reduced risk was observed among forestry workers, welders, and fishery workers for breast cancers diagnosed both before and after age 50. The SIRs for breast cancer did not vary substantially by histology. A significantly increased risk of breast cancer was observed among laboratory workers in the latest calendar period (1991–2005) compared with earlier periods (1976–1990 and 1961–1975). Occupations such as farming, forestry, driving, and gardening had low SIRs during all periods. Conclusions: The study suggests that the risk of breast cancer varies by occupation. Heterogeneity is also observed in some occupational categories according to age (before or after 50), histology, and calendar period.