A new muscle flap based on the ascending branch of the deep circumflex iliac artery is described. Twenty internal oblique muscle flaps have been dissected and studied in 10 fresh cadavers. This muscle flap has been used successfully as a free-tissue transfer in seven lower extremity defects. There was one loss of flap due to venous thrombosis. Other complications included a local wound abscess (one case), partial loss of skin graft (two cases), and arterial thrombosis (one case). There has been no donor-site morbidity. The donor scars are well concealed and no hernias have been observed, the longest follow-up being 9 months. The additional advantages of this flap include its thin, flat shape, excellent vascularity, and ease of application to areas about the ankle, with good aesthetic results. The disadvantages are (1) bloody and tedious dissection and (2) potential for abdominal weakness or hernia in the long run. This muscle flap appears to be excellent as a free flap for coverage of small- to moderate-sized defects of the distal lower extremity and as a pedicle flap for coverage of soft-tissue defects of the groin and anterior perineum.