To evaluate the likelihood of requiring major corrective surgery (MCS) after modified radical mastectomy (MRM), immediate reconstruction and radiation therapy (RT) to the reconstructed breast. The study population consisted of 62 patients who underwent MRM and immediate breast reconstruction between 1990 and 1999, had postoperative radiation and at least one follow-up visit or procedure > or = 2 months after radiation. Reconstruction consisted of a pedicled transverse rectus abdominis myocutaneous flap in 42 patients, latissimus dorsi flap in five, latissimus dorsi plus implant in six, and implant alone in nine. Median follow-up time after reconstruction was 13 months (range: 2-58) for non-implant patients and 10 months (range: 4-57) for implant patients. The primary endpoint was the incidence of major complications requiring MCS. Ten patients (16%) underwent MCS between 1 and 28 months after radiation (median in these patients of 8 months). 4/47 non-implant patients (9%) underwent MCS, compared to 6/15 implant patients (40%). Of patients followed > or = 6 months after RT, 0/38 non-implant patients underwent MCS within 6 months compared to 3/13 (23%) implant patients (p = 0.01); of patients followed for > or = 12 months after RT, the rates of MCS within 12 months were 1/24 (4%) and 2/7 (29%), respectively (p = 0.12). Patients who undergo immediate reconstruction after mastectomy using an implant followed by radiation have a high rate of subsequent MCS. The difference in the rate of MCS between the implant and non-implant groups is significant in early follow-up. Patients considering an implant followed by RT should be apprised of this increased risk. Prospective studies of these risks and the cosmetic outcomes are warranted.