Background: The aim of this study was to determine the proportion of patients with familial adenomatous polyposis (FAP) who had mutations in the desmoid region of the adenomatous polyposis coli (APC) gene that phenotypically expresses desmoid disease, and to determine the role for surgery in these patients. Methods: Data from the North West Region FAP database and case notes were analysed retrospectively. Results: Of 363 patients with FAP, 47 from ten families had APC mutations in the desmoid region 3′ to codon 1399. Of 22 patients undergoing surgery, 16 developed desmoids, and of these 12 had mesenteric desmoid disease. Complications from mesenteric desmoids were death (two patients), enterectomy (three), local resection (three), fistula (one), cholangitis and local resection (one), bowel obstruction (one) and bowel and ureteric obstruction (one). Preoperative polyp burden ranged from 0 to 100 in eight patients (median age 24.5 (range 16-39) years) and more than 100 in seven (median age 39 (range 31-64) years). One patient had no record of polyp burden. Conclusion: In individuals with 3′ APC mutations, abdominal surgery is associated with a 65 per cent risk of developing mesenteric desmoids. An alternative strategy might be to attempt to manage the polyps endoscopically. Copyright © 2007 British Journal of Surgery Society Ltd. Published by John Wiley & Sons Ltd.