DNA ploidy was determined by cytofluorometric analysis of paraffin-embedded malignant tissue from 96 Japanese patients in whom gastric carcinoma had invaded the serosa. Aneuploidy was found in gastric carcinoma tissue from 63 patients (66%). The postoperative 5-year survival rate of patients with aneuploid malignancy was significantly lower (13%) than those with diploid malignancy (36%) (p less than 0.05). A multivariate analysis of various clinical and pathologic factors showed that tumor size, lymph node metastasis, vascular invasion, and DNA ploidy were significant and independent factors, which correlated with prognosis.