To examine the associations between intakes of calcium, Vitamin D, and dairy foods and the risk of colon cancer, the authors analyzed data from a prospective study of 47,935 US male professionals, 40-75 years of age and free of cancer in 1986. Within this cohort, 203 new cases of colon cancer were documented between 1986 and 1992. After adjusting for age and total energy intake, the authors found that the intake of calcium from foods and supplements was inversely associated with colon cancer risk (relative risk (RR) = 0.58, 95% confidence interval (CI) 0.39-087 between high and low intakes of calcium). However, after adjusting for confounding variables, they found that the trend was no longer statistically significant (p = 0.22), and the relative risk for the highest quintile group of intake was attenuated: 0.75 (95% CI 0.48-1.15). Similar results were observed for total vitamin D intake; the age- and energy-adjusted relative risk was 0.54% (95% CI 0/34-0/85) for the highest versus lowest quintile group, and this was attenuated in the multivariate model (RR = 0.66, 95% CI 0.42-1.05). The inverse association was weaker for dietary vitamin D (RR highest vs. lowest quintile = 0.88. 95% CI 0.54-1.42) and strongest for vitamin D arising from vitamin supplements (RR = 0.48, 95% CI 0.22-1.02). Thus, it is possible that other components of multivitamin use rather than vitamin D accounted for the reduction in risk. Consumption of milk and fermented dairy products was not significantly associated with the risk of colon cancer; individuals consuming two or more glasses of "whole" or skim milk per day had a relative risk of 1.09 (95% CI 0.69-1.72), compared with those who consumed "whole or skim milk less than once a month. These prospective data do not support the hypothesis that calcium intake is strongly protective against colon cancer risk, although a modest association cannot be excluded.