Objective: To determine the relationships between the incidence rates of testicular and prostatic cancers and food consumptions in order to study the etiologic cause and the mechanism of the development of male genital organ cancer. Methods: The incidence rates of testicular and prostatic cancers in 42 countries (region) were correlated with the dietary practices in these countries. These data came from the cancer rate database (1988-1992) and the food supply database (1961-1990) provided by the Department of Environmental Health, Medical University of Yamanashi, Japan. Results: The incidence rates of testicular and prostatic cancers varied greatly from country to country but in China the rates of the both malignancies were lower than that of USA and Japan. This may be due to the difference in lifestyle, especially in dietary practices. Among the food items we examined, cheese was most closely correlated with the incidence of testicular cancer at ages 20-39, followed by animal fats and milk. The correlation coefficient (r) was the highest (r= 0.804) when calculated for cheese consumed during the period of 1961-1965 (maternal or prepubertal consumption). Stepwise- multiple-regression analysis revealed that cheese (1961-1965) made a significant contribution to the incidence of testicular cancer. Multiple coefficient ( r) is 0.920. As far as prostatic cancer was concerned, milk was most closely correlated (r=0.711) with its incidence, followed by meat and coffee. Stepwise-multiple-regression analysis identified milk, meat, butter and coffee as significant factors contributing to the incidence of prostatic cancer (R=0.993). The results of our study suggest a role of milk and dairy practices in the development of testicular and prostatic cancers. Objective: To determine the relationships between the incidence rates of testicular and prostatic cancers and food consumptions in order to study the etiologic cause and the mechanism of the development of male genital organ cancer. Methods: The incidence rates of testicular and prostatic cancers in 42 countries (region) were correlated with the dietary practices in these countries. These data came from the cancer rate database (1988-1992) and the food supply database (1961-1990) provided by the Department of Environmental Health, Medical University of Yamanashi, Japan Results: The incidence rates of testicular and prostatic cancers varied greatly from country to country but in China the rates of the both malignancies were lower than that of USA and Japan. This may be due to the difference in lifestyle, especially in dietary practices. Among the food items we examined, cheese was most closely correlated with the incidence of testicular cancer at ages 20-39, followed by animal fats and milk. The correlation coefficient (r) was the highest (r = 0.804) when calculated for cheese consumed during the period 1961-1965 (maternal or prepubertal consumption). Stepwise-multiple-regression analysis revealed that cheese (1961-1965) made The multiple coefficient (r) is 0.920. As far as prostatic cancer was concerned, milk was most closely correlated (r = 0.711) with its incidence, followed by meat and coffee. Stepwise-multiple- regression analysis identified milk, meat, butter and coffee as significant factors contributing to the incidence of prostatic cancer (R = 0.993). The results of our study suggest a role of milk and dairy practices in the development of testicular and prostatic cancers.