We conducted a prospective cohort study to evaluate the preventive effect of ginseng on the development of cancer in the population over 40 years old residing in Kangwha-eup from August 1987 to December 1992. Alnong 4, 634 persons (2, 362 men, 2, 272 women), 335 (7.6%) persons had died. Cancer accounted for 79 (22.8%) of the total death. Of 4, 634 persons eligible for analysis, 70.475 (3, 263) were ginseng intakes. Ginseng intakes had a decreased risk (RR=0.48, 95% Cl : 0.34~0.67) compared with non-intakes. The relative risk of cancer according to the kind of ginseng was 0.23 (95% Cl : 0.08~ 0.63) for fresh ginseng extract intakes. There was a decrease in risk with rising the frequency of ginseng intake, showing statistically significant dose-response relationship. The longer the duration of ginseng intake or the greater the total number of ginseng consumed, the lower the risk. Newly diagnosed cancer cases have been identified: 42 stomach, 24 lung, 14 liver and 57 at other sites. The relative risks of ginseng intakes were 0.34 (95% Cl 0.19~0.60) in gastric cancer and 0.27 (95% Cl : 0.12-0.60) in lung cancer. Among ginseng preparations, fresh ginseng intakes were significantly associated with the decreased risk of gastric cancer (RR: 0.19, 95% Cl : 0.04~0.98). These results strongly revealed that Panax Ginseng C.A. Meyer (Korean ginseng) has preventive effect against cancer.