The authors evaluated rectus abdominis muscle function after deep inferior epigastric perforator (DIEP) flap elevation. Fifteen consecutive patients who were operated on for breast reconstruction with a free DIEP flap were included in the study. A turn-amplitude electromyographic analysis was used. For each patient, the muscle activity was recorded in the portion of the muscle that was split for the epigastric perforator vessel dissection, and also in the similar portion of the contralateral nondissected muscle. A first electromyographic examination was carried out soon after surgery (mean follow-up, 9 weeks), and a second electromyographic examination was carried out at a later date (mean follow-up, 15 months). The mean activity of the dissected muscles was 50 percent of the activity of the nondissected muscles at the first electromyographic examination and 70 percent at the second electromyographic examination. The authors suggest that the DIEP flap procedure induces a partial denervation of the rectus abdominis muscle in the area of dissection and that reinnervation occurs over time because the entire width of the muscle and sufficient segmental motor innervation are preserved.