This study investigated the performance status, mental status, and prognosis of 24 patients older than 80 years whose gastric cancer had been managed surgically during the past 6 years, and 21 patients who were observed conservatively. The advantages and disadvantages of surgery for elderly patients with gastric cancer is discussed. The 3-year survival rate for patients with advanced gastric cancer was 31% for those surgically treated and 0% for those observed conservatively. The difference is statistically significant. The survival rate for patients with early gastric cancer was 62.5% in the surgical treatment group and 33.3% in the conservative observation group, a difference that is not significant. Decline in performance status and deterioration of mental status after open surgery were slight, and the survival rate for patients treated surgically was significantly higher than for conservatively observed patients, regardless of performance status and whether mental status had deteriorated. On univariate and multivariate analyses, the presence or absence of open surgery and macroscopic classification were the only significant prognostic factors, whereas performance status and the presence or absence of mental deterioration were not significant prognostic factors. These results suggest that surgical treatment should not be discouraged even for patients older than 80 years.