Many epidemiological studies have provided support for the hypothesis that type II diabetes can increase the risk of colorectal cancer, but time trends, geographical distributions and host factors for the two diseases remain largely to be clarified. To address these issues, we investigated the epidemic pattern of colon cancer and type II diabetes among Japanese in Japan (J-Japanese), with consideration of the westernization of dietary habits. Over the last three decades, the increase in crude mortality rates of colon cancer from the Vital Statistics has closely paralleled the increment in prevalence rates (PRs) from hospital based surveys of diabetes. Age-standardized incidence rates (ASIRs) for colon cancer among Japanese in the United States (US-Japanese) were higher than those among J-Japanese and almost the same as those among US-Whites, while PRs for type II diabetes among US-Japanese were the highest in the three populations. Correlation analysis showed that PRs for type II diabetes had a positive association with ASIRs for colon cancer among the combination of Japanese and US-Japanese (r=0.79, p<0.01). Since 1950, intake of milk, meat, eggs and fat/oil has increased, while that of rice and potatoes has gradually decreased. Our findings indicate that the increment of ASIRs for colon cancer among J-Japanese might be closely associated with the increment of PRs for type II diabetes, reflecting the westernization of food intake.