Purpose. -To compare the healthcare costs of women with unilateral breast cancer who underwent contralateralprophylactic mastectomy (CPM) with those of women who did not. Methods. -We conducted a retrospective study of 904 women treated for stage I-III breast cancer with or without CPM. Women were matched according to age, year at diagnosis, stage, and receipt of chemotherapy. We included healthcare costs starting from the date of surgery to 24 months. We identified whether care was immediate or delayed (CPM within 6 months or 6e24 months after initial surgery, respectively). Costs were converted to approximate Medicare reimbursement values and adjusted for inflation. Multivariable regression analysis was performed to evaluate the effect of CPM on total breast cancer care costs adjusting for patient characteristics and accounting for matched pairs.