Cell nuclear DNA content was determined by flow cytometric analysis in 270 patients with deeply infiltrating (beyond the submucosa) cancer, so-called advanced gastric cancer. Aneuploidy was observed in 150 cases (55.6%). Multivariate analysis showed that the DNA ploidy pattern was the third significant prognostic factor behind peritoneal dissemination and liver metastasis. The 5-year survival rate of diploid patients (62.9%) was significantly higher than that of aneuploid patients (22.7%) (P less than 0.01). This trend was most clear in patients with Stage III and IV tumors. Among aneuploid cases the high DNA index group indicated a worse prognosis than the low DNA index group. It was thus assumed that the DNA ploidy pattern was a useful prognostic indicator of advanced gastric cancer.