We report clonal chromosome abnormalities in short term cultures of seven gastric or esophageal adenocarcinomas and two squamous carcinomas of the esophagus and EG junction. The most consistent aberration encountered was a del(3) (q13.2q23) seen in six of nine tumors. This finding, together with a survey of published cytogenetic literature, suggested that del(3q) is the most common cytogenetic abnormality, and hence possibly of primary significance, in these tumors. In addition to del(3q), rearrangements affecting 1p13 (two cases), 6q15-q23 (two cases), 7p22 (two cases), 7q22 (two cases), and 11p11.2-p14 (three cases) were seen. Cytogenetic evidence for gene amplification in the form of homogeneously staining region (hsr) was seen at 9q13 in two cases.