To obtain a relevant index of the impact of cancer on the Japanese population, considering curable cases as well as mortalities, the probability of developing cancer in the entire life span of a Japanese was estimated. A method based on the cumulative risk of cancer was employed to estimate the probability. This cumulative risk method gave a lifetime probability of developing cancer in any site of 52 % for males and 31 % for females in 1994 up to 85+ years of age. and for the average life expectancy of Japanese, 77 years for males and 84 years for females, 32 % and 26 % respectively. The estimated probabilities provide reasonable and practical indices of the impact of cancer today. This method can be also applied to local estimation if population-based cancer registry data are available.