The clinicopathologic and immunohistochemical features in 120 cases of gastrointestinal stromal tumor (GIST) were reviewed. Excluding 24 cases of gastric schwannoma, 96 cases of GIST consisting of 62 benign tumors and 34 sarcoma (low grade, 17; high grade, 17), with 9 cases arising in the esophagus, 57 in the stomach, 28 in the small intestine, and 2 in the colon, were studied. All esophagus and colon tumors were benign and resembled a conventional leiomyoma histologically. However, the gastric and small intestine benign tumors mostly showed histologic features of cellular or epithelioid leiomyoma. Immunohistochemically, desmin caused a positive reaction in all esophagus and colon tumors, but only 26% of gastric and small intestine tumors. However, muscle-specific actin (HHF35) caused a positive reaction in most GIST (92%). The 10-year survival rates of the patients with gastric sarcoma and those with intestinal sarcoma were 74% and 17%, respectively. These results showed that histologic and immunohistochemical features were distinctly different, depending on the location in the gastrointestinal tract; that most GIST, excluding schwannoma, had smooth muscle differentiation; and that sarcomas had a more favorable prognosis when they occurred in the stomach rather than the intestine.