We reconstructed a large chest wall defect, resulting from the resection of a locally advanced breast carcinoma, using an external oblique myocutaneous flap. The patient, a 58-year-old Japanese woman, presented with an inoperable breast carcinoma (Stage IV). Combination chemotherapy with cyclophosphamide (CPA) and epirubicin hydrochloride (EPI) resulted in a reduction in size of both the primary tumor and the metastatic lesions. However, the patient continued to experience purulent discharge accompanied by an unpleasant odor, as well as contact bleeding from the residual breast lesion. To address these complaints, we removed much of the remaining tumor surgically. The resulting skin defect measured 440 cm(2) and was covered using an external oblique myocutaneous flap. The patient's postoperative course was excellent, and she was still alive and well after 40 months of chemotherapy. This case is a demonstration of the effectiveness of the external oblique myocutaneous flap for the coverage of large ipsilateral chest wall defects.