To promote a cancer prevention program at hospital, we started the hospital-based epidemiologic research program at Aichi Cancer Center (HERPACC) in 1988. Because patients visiting hospitals are very concerned not only about their own health condition but also practical way of disease prevention, we consider outpatients, especially those free of cancer, as ideal targets to make a model program and a practical cancer prevention strategy for general people. To confirm risk and protective effects of lifestyle factors like dietary habits, smoking and drinking, and exercise on cancer in Japanese, we have been undertaking large-scale case-referent comparative studies of main cancer sites (stomach, colorectal, lung, breast and uterine cancers) using the data generated by HERPACC. The risk of respiratory tract cancer was definitely elevated by habitual smoking and that of upper digestive tract cancer by combined habitual smoking and drinking. Frequent intake of raw vegetables and/or fruit in contrast reduced the risk of lung cancer among smokers. Current obesity was positively associated with risk of post-menopausal breast cancer, recently on the increase in Japan. However, all sites of cancer were linearly decreased with frequency of exercise in both males and females. Based on these pieces of evidence and other main results obtained from the HERPACC studies, prevention trials with provision of information about protective and risk factors for main sites of cancers to outpatients have been planned in parallel to continuation of HERPACC.