This study assesses the usefulness of the omentum in the reconstruction of complex perineal defects, following abdominoperineal resection or pelvic exenteration, for anorectal malignancy. Between 2000 and 2008, 70 patients (mean age: 59 years) with anorectal malignancy underwent abdominoperineal resection (n = 57) or pelvic exenteration (n = 13) and were reconstructed by primary repair alone (n = 13), primary repair with omentum (n = 16), myocutaneous flap alone (n = 28), or myocutaneous flap with omentum (n = 13). Patients with and without omental flaps were compared by Student t test and chi2 analysis. Omental flaps were based on a single pedicle, tunneled in the retrocolic plane lateral to the ligament of Treitz, and transposed across the sacrum to the pelvic floor. In total, 29 patients had pelvic floor and perineal reconstruction with the omentum, and 41 patients had reconstruction without the omentum. Incidence of major pelvic complications (abscess, urinoma, deep vein thrombosis, flap dehiscence, hernia, bowel obstruction, fistula) was greater in the "no omentum" group (25/41 patients, 61%), compared with the "omentum" group (6/29 patients, 21%) (P < 0.01). No differences were observed regarding age, stage, incidence of radiotherapy, blood loss, length of stay, or mortality. Use of the omentum as a primary flap, or in combination with a myocutaneous flap, in the reconstruction of complex perineal defects, is associated with a decreased incidence of postoperative complications, strongly supporting the use of the omentum in pelvic floor reconstruction.