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Importance Long-term follow-up studies regarding the safety of risk-reducing mastectomy (RRM) in terms of cancer risk and surgical complications among women with germline pathogenic variants (gPVs) in BRCA1 or BRCA2 (BRCA1/2) are scarce. Objective To analyze cancer risk and surgical complications after RRM. Design, Setting, and Participants This nationwide cohort study investigated 1208 Swedish women with a confirmed gPV in BRCA1/2 without previous breast cancer identified through the Swedish Cancer Genetic Units between March 31, 1994, and January 2, 2019. Data were extracted from the National Patient Care Register, the Cancer Register, and the Cause of Death Register. Women were followed up from the date of RRM (RRM group) or genetic testing (no RRM group) until breast cancer diagnosis, death, emigration, or end of follow-up (December 31, 2023). Main Outcomes and Measures Breast cancer incidence was calculated per 10 000 person-years, with women undergoing RRM contributing person-years to the no RRM group until RRM, and women with occult breast cancer contributing breast cancer cases to the no RRM group. Results In the RRM group (507 women; median age at RRM, 39.7 years [range, 19.6-72.1 years]), 1 woman developed breast cancer, corresponding to a breast cancer incidence of 2 cases per 10 000 person-years. In the no RRM group (701 women; median age at genetic testing, 50.6 years [range, 4.3-93.6 years]), 112 women developed breast cancer, corresponding to a breast cancer incidence of 162 cases per 10 000 person-years. At RRM, 17 of 507 women (3.4%) received a diagnosis of occult breast cancer. In the RRM group, 296 of 507 women (58.4%) underwent simple mastectomy, 143 of 507 (28.2%) underwent nipple-sparing mastectomy, and 68 of 507 (13.4%) underwent skin-sparing mastectomy. Most women (382 of 507 [75.3%]) underwent implant-based breast reconstruction, with only 73 of 507 (14.4%) undergoing autologous tissue reconstruction with or without implants. Early major surgical postoperative complications associated with reoperation occurred in 19 of 507 women (3.7%). Conclusions and Relevance In this cohort study of 1208 women with a gPV in BRCA1/2, the risk of developing breast cancer or early major surgical complications after RRM was very low. The low occurrence of primary breast cancer precluded meaningful statistical comparisons between different RRM techniques.