The chromosomes of a human gastric leiomyosarcoma were studied in preparations from short-term cultures. The tumor had a triploid-near-triploid modal population characterized by extensive numerical and structural changes. Of these deviations, del(1)(p12-13), monosomy 14, and underrepresentation of chromosomes 18 and 22 were abnormalities in common with two of the three previously studied leiomyosarcomas of the small bowel.