A retrospective review of the treatment of 15 breast cancer patients who received postoperative radiotherapy after a mastectomy and transverse rectus abdominis myocutaneous (TRAM) flap breast reconstruction was undertaken to determine the effects of postoperative irradiation on flap viability and cosmesis. Fourteen patients had pedicle TRAM flaps, and one patient had a free TRAM flap. Surgical complications, acute and chronic side effects of radiotherapy, and cosmetic outcome were evaluated. The median interval between the TRAM flap procedure and radiotherapy was 7 months. The median total radiation dose was 60 Gy. All patients underwent three-dimensional radiotherapy treatment planning to determine the optimal dose distribution. Mild erythema developed in 9 patients (60%), moderate erythema developed in 2 (13%), and severe erythema developed in 1 (7%). Dry desquamation developed in 6 patients (40%), whereas moist desquamation developed in none. At median follow-up of 26.4 months, only 2 (13%) of the 15 patients had fat necrosis within the TRAM flap that was not present before radiotherapy. Fourteen patients (93%) retained their flap, and 13 patients (87%) rated their cosmetic outcome as "good" to "excellent." We conclude that TRAM flaps can be irradiated with few complications and acceptable cosmetic results.