To determine factors associated with a favorable long-term prognosis in gastric leiomyosarcoma, we retrospectively reviewed the medical records of 93 Mayo Clinic patients with this biopsy-proven tumor diagnosed during the 25-year period from 1964 through 1988. Six patients who had Carney's triad (gastric epithelioid leiomyosarcoma, pulmonary chondroma, and functioning extra-adrenal paraganglioma) were excluded from data analysis. The other 87 patients participated in follow-up until death or for a median duration of 5.8 years for those who were alive at the conclusion of the study. The most common symptoms at the time of initial assessment were abdominal pain (51%), melena (36%), and weight loss (16%). Most often, the tumor was located in the greater curvature (25%), fundus (20%), or lesser curvature (16%) of the stomach. Two percent of patients had tumors at multiple sites. All 87 gastric leiomyosarcomas were histologically confirmed; 38% were grade 1, 37% were grade 2, and 25% were either grade 3 or grade 4. Metastatic involvement was noted in 15% of patients at the time of diagnosis. The 5- and 10-year survival rates were 45% and 34%, respectively, and the 5- and 10-year tumor recurrence rates were 57% and 65%, respectively. Variables that were associated with long-term survival were low histologic grade of the tumor, absence of metastatic lesions, and small tumor size (P < 0.01); variables such as site of the tumor, initial symptoms, age, and sex provided no significant additional prognostic information.