Recently, high aged patients with malignancies have increased in number. When cancer chemotherapy is applied for the high aged patients, kinds or doses of anti-cancer drugs must be more carefully selected or decided than for younger patients, because it is said that the side effects of anti-cancer drugs would easily induce irreversible organ disorders and death in high aged patients. The effects of cancer chemotherapy were compared between high aged patients (over 75 years) and younger patients (5 decade years) with special reference to side effects. The patients underwent cancer chemotherapy were 79.7% of high aged patients and 93.6% of younger. The reasons why cancer chemotherapy was not carried out were high age (5.6% of high aged patients), poor general conditions (7.0% in high aged, 2.3% in younger) and post operative complications (7.0% in high aged, 3.2% in younger). The proportion of patients suffered side effects was almost same in both groups. Dead cases caused by side effects of anti-cancer drugs were 5 in high aged patients (4.4%) and 7 in younger (3.4%). The reason why the proportion of side effects in both groups was not different was that the doses of anti-cancer drugs given for high aged patients were reduced to 80-90% of those for younger patients.