The etiology of lower abdominal bulge following breast reconstruction with the DIEP flap is uncertain. Most studies report an incidence that ranges from 0.7% to 5%. The purpose of this study was to review a set of factors that may predispose to a lower abdominal bulge. This was a retrospective review of 123 women who had breast reconstruction with the DIEP flap over a 4-year period. The reconstruction was unilateral in 93 women and bilateral in 30 women, totaling 153 flaps. Etiologic factors that were evaluated included patient age, diabetes mellitus, tobacco use, previous abdominal operations, unilateral or bilateral reconstruction, previous childbirth, aponeurotic plication to improve the natural abdominal contour, and use of Marlex mesh. A lower abdominal bulge occurred in 5 of the 123 women (4%), 2 following 30 bilateral reconstructions (6.6%) and 3 following 93 unilateral reconstructions (3.2%). Analysis of the factors for all women demonstrated diabetes mellitus in 1 (0.8%), tobacco use in 9 (7.3%), a prior abdominal operation in 55 (44.7%), previous childbirth in 95 (77%), aponeurotic plication in 49 (40%), and use of Marlex mesh in 4 (3.3%). Statistical analysis did not show any significant association between the explanatory factors and the occurrence of a lower abdominal bulge, except for a weak trend in women who had not been pregnant (P = 0.08). The results of this study demonstrate that the occurrence of a lower abdominal bulge following the DIEP flap is a random event that can occur in anyone. Pregnancy may confer a preventative effect as the collagen fibers strengthen to overcome the stretching forces. Techniques for prevention and treatment include intraoperative assessment of the anterior rectus sheath, use of an adjuvant material for reinforcement if unstable, and vertical plication for bulge repair.