Leiomyosarcomas are malignant tumors of smooth muscle. Leiomyosarcomas of the large intestine are rare, with an incidence of less than 0.1% of all colorectal malignancies. A 70-year-old woman was admitted to the hospital with lower abdominal pain and hematochezia. The abdominal CT scan revealed a solid mass in the sigmoid colon and intussusception with a lead point. Surgical excision of the sigmoid colon mass was performed. The patient was diagnosed with a leiomyosarcoma originating from the sigmoid colon. Few cases of primary sigmoid colon leiomyosarcoma presenting as an intussusception have been reported in the medical literature. We report here on a case of complete surgical resection for a leiomyosarcoma of the sigmoid colon and this presented as intussusception. (Korean J Gastrointest Endosc 2010;40:270-274)