To investigate chromosome aberrations and their role in the genesis and development of primary gastric cancer. Methods: An improved, direct chromosome preparation from solid tumors was adopted for G-banding analysis followed by FISH on decolored G-banding chromosomes so that chromosome aberrations could be confirmed at DNA level. Results: A total of 28 primary gastric cancer specimens were studies. Case 1 and case 2 had simple chromosome numerical changes: 49, XY, +2, +8, +9 and 48, +8, +20, respectively. All but case 1 and 2 had complicated chromosome abnormalities. Chromosome structural of frequent occurrence involved del (7q)(21/26), (delOp)(14/26), del (lp)(ll/26) and del (17p)(10/26). The chromosome abnormalities could be simple and complicated. In former, numerical changes involving 1 to 3 chromosome could be observed. Trisomies 8 and 9 might represent a ytogenetic subgroup of primary gastric cancer. In the later, the del (7q) was the most consistent aberration. 7q32-qter was the commonly lost segment. Conclusion: Numerical and structural alterations of chromosomes are present in primary gastric cancer. Del (7q) is one of the structural change characteristic of primary gastric cancer. In the 7q32qter fragment, a tumor suppressor gene probably exists and it may have close relation to the genesis and progression of gastric cancer.