BACKGROUND: Bilateral prophylactic mastectomy significantly decreases breast cancer risk, but complications of the procedure have only been described in single-site studies. We describe the frequency and type of complications in women who underwent bilateral prophylactic mastectomy in a multisite community-based cohort. METHODS: Women aged 18-80 years undergoing bilateral prophylactic mastectomy without a personal history of breast cancer at one of six health plans were eligible. We identified women from automated data sources, then reviewed hospital data, ambulatory notes, and other chart elements to confirm eligibility and obtain all charted information about complications and surgeries performed after prophylactic mastectomy, including reconstructive procedures. Reconstructions were characterized by type (implant vs. tissue graft). Complications were noted for a 1-year period after any surgical procedure. RESULTS: We identified 269 women with prophylactic mastectomy who were followed for a mean of 7.4 years. Their mean age was 44.9 years. Nearly 80% undertook reconstruction, most with prosthetic implants. One or more complications occurred in 64%. The most common complications were pain (35% of women), infection (17%), and seroma (17%). Women with no reconstruction had fewer complications (mean of .93) than women who had implant (2.0) or tissue graft (2.4) reconstruction procedures (differences from no reconstruction: 1.07 [95% confidence interval = 0.36 to 1.77] and 1.50 [95% confidence interval = 0.44 to 2.56] respectively). Delay of reconstruction after mastectomy was associated with a borderline-significant higher risk of complications (80.6%) compared to simultaneous reconstruction (64.0%, P = .055). CONCLUSION: We found that almost two-thirds of women undergoing bilateral prophylactic mastectomy had at least one complication following surgery. Further work should be done to minimize and to understand the effect of complications of bilateral prophylactic mastectomy.