Desmoid tumors are locally invasive, nonmetastasizing fibrous tumors most frequently seen in patients with familial polyposis coli (FPC). Of 325 patients with FPC treated at the Cleveland Clinic, 29 (8.9%) were found to have a total of 36 desmoid tumors. These tumors occur in young patients (mean age: 29.8 years), particularly women (ratio 3:1), and most appeared after previous colectomy (86%). The majority (72% of all desmoids, 90% of patients) were located within the abdomen, specifically within the mesentery of the small intestine. In most cases, attempts at surgical resection were followed by recurrence, and other previous treatments were similarly ineffective. Six of the 29 patients (21%) died from the desmoid and three died from other causes. The recent use of sulindac (Clinoril) has produced some early encouraging results in four patients with these tumors that have proven so difficult to treat in the past.