As immediate breast reconstruction with rectus abdominis and latissimus dorsi myocutaneous flaps has become a recognized technique for patients requiring mastectomy, concerns have arisen regarding the detection and treatment of locoregional recurrence of breast cancer. Because most recurrences develop in the residual native skin of the chest wall following a mastectomy, breast reconstruction procedures involving the placement of a subpectoral prosthesis are unlikely to interfere with postoperative cancer surveillance. Myocutaneous flaps, however, transpose blocs of soft tissues into the mastectomy site. This study was done to evaluate the influence of a myocutaneous flap on the subsequent diagnosis and treatment of locoregional recurrence of breast cancer. Data were obtained from 161 patients with breast cancer who had immediate reconstruction with a myocutaneous flap between 1982 and 1990. Of the 161 patients reviewed, 120 had primary mastectomy with immediate reconstruction; 41 patients had salvage mastectomy and immediate reconstruction after failed conservative surgery and radiation therapy. Modified radical mastectomy was performed on all patients. Either a rectus abdominis (n = 65) or latissimus dorsi (n = 97) myocutaneous flap breast reconstruction was performed. Recurrent tumor was observed in 17 of the 161 patients reviewed (10.6 percent). Fourteen of the 17 recurrences occurred in 120 patients having primary mastectomy and immediate reconstruction for a rate of 11.7 percent; 3 of 41 patients (7.3 percent) who had salvage mastectomy and flap reconstruction developed recurrences. Of the 17 recurrences, 6 patients were stage II, 10 were stage III, and 1 was stage IV. All 17 patients who developed a recurrence had invasive breast cancer, with infiltrating and inflammatory tumors predominating. All locoregional recurrences of breast cancer developed within the native skin and subcutaneous tissues adjacent to the mastectomy and flap reconstruction site. Recurrences were seen as rapidly as 2 weeks or as long as 3.8 years (mean 1.4) after the mastectomy and flap reconstruction. Overall mean follow-up for the entire group of 161 patients was 5.4 years. Thirteen of the 17 patients (76.5 percent) developed distant metastases either concomitantly with the locoregional recurrence or within 4.3 years (mean 1.7). From an oncologic viewpoint, the technique of myocutaneous flap breast reconstruction with rectus abdominis or latissimus dorsi flaps appears to be a safe one. An analysis of locoregional recurrence of breast cancer in patients undergoing primary mastectomy or salvage mastectomy with myocutaneous flap breast reconstruction did not show concealment by the flap of any recurrent tumor.(ABSTRACT TRUNCATED AT 400 WORDS)