We did a retrospective study to assess the influence of age on the prognosis in 1,537 patients with gastric cancer and who underwent gastrectomy. The patients were classified into 7 groups by age at the time of surgery, and the relative survival rates were calculated after correcting for each patient's sex, age, and the operative calendar year, based on the life table data for the general Japanese population. The overall prognoses in patients under age 30 and over age 80 years were poor (for ages under 30 years, 30-39, 40-49, 50-59, 60-69, 70-79, and over 80 years, the 5-year survival rates were 32.1%, 55.9%, 54.8%, 54.3%, 48.6%, 50.8%, and 31.5%, respectively). The poor prognoses in the youngest patients could be attributed to a high frequency of aggressive stage of the tumor. After curative gastrectomy, although the prognoses were excellent for every category in the first and second postoperative year, patients over age 80 years had a relatively poor prognosis after the third postoperative check-up. The poor prognoses in the oldest patients were attributed to the number of deaths due to other diseases. We conclude that for the very young or old subjects, age is a significant prognostic factor for those treated by gastrectomy for gastric cancer.