INTRODUCTION: Abdominal desmoid tumors are locally aggressive tumors that develop in familial adenomatous polyposis (FAP) patients, within the mesentery or abdominal wall. The understanding and implications of the treatment regimens are evolving. AIM: To assess the course, treatment, and outcomes of FAP and non-FAP abdominal desmoids and their related genetic alterations. METHODS: Retrospective cohort study. Demographics, tumor characteristics, oncological and surgical history, complications, genetic-testing, and mortality data were retrieved from two tertiary referral centers. RESULTS: Sixty-two patients were identified (46 FAP and 16 non-FAP). Thirty-eight patients (61.3%) underwent surgical procedures (12 urgent and 26 elective). Out of 33 tumor resections, 39.4% recurred. Hormonal therapy, COX-inhibitors, chemotherapy, imatinib, and sorafenib were used in 35 (56.4%), 30 (48.4%), 18 (29.1%), 7 (11.3%), and 8 (12.9%) of patients, respectively, with a 2 year progression-free survival of 67.8%, 57.7%, 38.4%, and 28.5%, respectively. Forty-one patients (66.1%) suffered complications: bowel obstruction (30.6%), hyperalimentation (14.5%), ureteral obstruction (12.9%), perforation (11.3%), abscess formation (3.2%), and spinal cord compression (3.2%). Non-FAP patients carried pathogenic mutations in and . CONCLUSIONS: Abdominal desmoids are mostly FAP-related and are associated with severe outcomes. We also report a group of non-FAP abdominal desmoids, which includes patients with additional cancer-related gene alterations. This interesting group should be further explored.