Background: A relation between abdominal obesity and colorectal tumor development has been reported repeatedly, and is believed to be more remarkable in man than in women. However, the details vary depending on scientific reports. This may be due at least partly to the selected surface anthropometric index in addition to the influence of gender and ethnic groups. To cope with this, we considered a new index of abdominal obesity and evaluated its risk prediction potential. Materials and Methods: Six hundred ninety five Japanese (262 women and 433 men) who had a colonoscopy were studied. The new index was named as waist circumference to height index (WHI) and was calculated by the formula of waist circumference (cm)/height (m)/height (m). Biochemical and lifestyle factors were investigated preceding the colonoscopy. Statistical analysis was performed using SPSS for Windows. Results: Increase of WHI was associated with altered metabolism of carbohydrate and lipid in both women and men. WHI was positively related with the development of colon tumor of women, while not with that of men. Logistic regression analysis performed for stratified age groups (45-54, 55-64 and 65-74 years) showed that WHI significantly increased odds ratio to 1.31 (CI 1.05-1.64 p=0.01) in women of 55-65 years. In contrast, in men this index WHI reduced the odds ratio insignificantly, while low density lipoprotein and triglyceride significantly increased the odds ratio to 1.01 (CI 1.00-1.03 p=0.02) in the 55-65 year group and to 1.02 (CI 1.00-1.03 p=0.02) in the 45-55 year group. Conclusions: In Japanese the risk factors for colon tumor development are different between women and men. WHI is a simple and efficient predictor of colon tumor risk in Japanese women and may be used to select those who should have colonoscopy.