A prospective study of cancer and coronary heart disease (CHD) in 8,006 Hawaiian Japanese men, aged 45-68 years, showed that serum cholesterol levels below 180 mg/dl predicted low rates of CHD and high rates of colon cancer. Men with colon cancer had lower mean serum cholesterol levels than did other members of the cohort, including those with cancer at other sites. The lowest serum cholesterol levels were obtained from men who died as a result of colon cancer. The lack of such an association with other cancers and the persistence of this inverse association in colon cancer patients diagnosed 5-9.9 years after examination suggest that the low serum cholesterol was not due to preexisting disease. Right colon tumors showed the strongest inverse association with serum cholesterol. The differences between CHD and colon cancer in respect to serum cholesterol indicate that different subsets of the westernized Japanese population are affected.