The fibromatosis (desmoid tumor) is histologically benign fibrous neoplasm arising from the musculoaponeurotic structures through out the body, but that shows locally aggressive growth. Common anatomic sites includes the limbs, trunk and mesentery. Fibromatoses arising in the neck have been reported rarely. If the tumors are occurred in the neck, complete resection is often difficult, because of its locally infiltrative nature. Therefore radiotherapy, chemotherapy and hormonal therapy are occasionally needed to reduce local recurrence. We report herein a case of fibromatosis arising in the left supraclavicular region with infiltration to surrounding tissues, which was successfully treated by complete surgical excision and postoperative adjuvant radiotherapy.