The aim of this study was to evaluate whether the dissection of the vascular pedicle of the deep inferior epigastric perforator (DIEP) flap could induce secondary muscle atrophy. Evaluation of the rectus abdominis muscle was performed using ultrasonography, and the muscle thickness was measured as an expression of muscle substance. This was performed at 4 levels: below the xiphoid process, at the umbilicus level, above the symphysis, and between the 2 last mentioned (central zone). The results were expressed as the ratio of the muscle thickness on the operated side where dissection of the vascular pedicle was performed to the thickness of the contralateral not operated muscle. Thirteen patients were included with a mean follow up of 20 months (range, 7-42 months). The combined measurements showed that the thickness of the muscle as a whole was significantly reduced on the operated side compared with the opposite side. Broken down to the specific levels, the greatest reduction in thickness, approximately 10%, was found at the xiphoid process and above the symphysis. We conclude that performing the dissection of the vascular pedicle of the DIEP flap gives a small but significant degree of muscular atrophy.