A 46-year-old man presented to our hospital for further examination following a positive fecal occult blood test. He also had a painless, palpable scrotal mass that had been present for several years, but he had not previously sought treatment. Colonoscopy demonstrated multiple adenomatous polyps and colon cancer ; when taken together with his family history, these findings led to the diagnosis of familial adenomatous polyposis. A computed tomography scan revealed a right intrascrotal tumor, and the patient was referred to our department. Together with digestive surgeons, we carried out scrotal mass resection and colectomy under general anesthesia. On scrotal exploration, a large, solid mass was identified ; it was separate from the testis and epididymis. Although the mass was adhered to the surface of the corpus cavernosum penis, we were able to completely resect the mass along with part of the corpus cavernosum penis. The tumor was composed of abundant collagen fibers and mature fibroblasts. Histopathology revealed the right scrotal mass to be a desmoid tumor. The patient is alive with no evidence of disease 24 months after surgery.