Mounting evidence suggests that high circulating levels of insulin might be associated with increased colorectal cancer risk. The glycemic effects of diets high in refined starch may increase colorectal cancer risk by affecting insulin and/or insulin-like growth factor-I levels. We examined the association between dietary intake and colorectal cancer risk in a cohort of 49 124 women participating in a randomized, controlled trial of screening for breast cancer in Canada. Linkages to Canadian mortality and cancer databases yielded data on mortality and cancer incidence up to December 31, 2000. During an average 16.5 years of follow-up, we observed 616 incident cases of colorectal cancer (436 colon cancers, 180 rectal cancers). Rate ratios for colorectal cancer for the highest versus the lowest quintile level were 1.05 (95% confidence interval [CI] = 0.73 to 1.53; P(trend) =.94) for glycemic load, 1.01 (95% CI = 0.68 to 1.51; P(trend) =.66) for total carbohydrates, and 1.03 (95% CI = 0.73 to 1.44; P(trend) =.71) for total sugar. Our data do not support the hypothesis that diets high in glycemic load, carbohydrates, or sugar increase colorectal cancer risk.