Nine cases of gastrointestinal leiomyosarcoma were studied by ultrasound. Abdominal sonogram disclosed a large lobulated iso or hypoechoic mass containing a few or multiple central sonolucent cavitations in seven cases. Two cases arising from mesentery and abdominal wall were hypoechoic mass without central sonolucent area. These central sonolucent areas were confirmed to be necrotic or hemorrhagic cavities in the solid mass pathologically. Although not pathognomonic, a large lobulated exophytic gastrointestinal mass with central sonolucent area strongly suggests the diagnosis of leiomyosarcoma.