PURPOSE: Unexpected vascular anomaly can make the surgeon embarrassing and even affects on the operative results of free flap reconstruction. We experienced one case of abnormal course of deep inferior epigastric vessels during the elevation of rectus abdominis musculocutaneous free flap for breast reconstruction. METHODS: A 38-year-old female patient who had modified radical mastectomy on her left breast underwent delayed breast reconstruction with rectus abdominis musculocutaneous free flap. RESULTS: Flap elevation was performed in the traditional manner. During the flap elevation, it was detected that the deep inferior epigastric vessels ran between the rectus abdominis muscle and anterior rectus sheath along the midline after traversing the rectus muscle. The reconstructive surgery was successful and there were no postoperative complications. CONCLUSION: This is the first case reported in Korea. We should always know about the possibilities of unexpected anomaly that we can encounter.