OBJECTIVE Perineal hernias are infrequent complications of abdominoperineal operations with estimated historic prevalences (from the era where the perineal wound was left open) ranging from 0.6 to 7 percent. The purpose of this study was to identify the modern prevalence of postoperative perineal hernias, factors that may contribute to their development, and examine the methods of repair. METHODS The Mayo Clinic patient database (1990-2000) was interrogated for the following data identifiers: incisional hernia, perineal hernia, abdominoperineal resection, proctocolectomy, and partial or total pelvic exenteration. All surviving patients were followed up to December 2005. The retrieved patient data was retrospectively analyzed. RESULTS Of a total of 3,761 patients who underwent abdominoperineal resection (including nonrestorative proctocolectomy and pelvic exenteration) during the study period, 8 developed a perineal hernia (5 females). The median age at hernia presentation was 76 (range, 69-84) years, representing a median interval of 22 (range, 1-60) months from the original operation. All were smokers (> or =15 pack years) and five had received chemoradiotherapy for their original diagnosis. The commonest prevalence was found in patients who had undergone abdominoperineal resection (5/1,266) or pelvic exenteration (2/1,334). Only 1 of 1,161 patients developed a perineal hernia after proctocolectomy despite most being on perioperative immunosuppression for inflammatory bowel disease. Abdominal exploration and repair was performed in four patients whereas four underwent perineal repair (2 of each with mesh). None have recurred with a median follow-up of 36 (range, 6-60) months. CONCLUSIONS Perineal hernias are rare complications of abdominoperineal surgery with a more common prevalence after cancer operations. Smoking and chemoradiotherapy, but not corticosteroid immunosuppression, may be factors. The abdominal approach has advantages over the perineal approach, but both are suitable with good medium-term results.