A high intake of calcium, vitamin D, or specific dairy products is thought to reduce the incidence of colorectal cancer. The association of these nutrients and foods with the occurrence of colorectal adenomas, precursors of cancer, was studied in two large US cohort studies. Cases were patients with a diagnosis of adenomatous polyps of the left colon or rectum (331 men, 1986-1990; 350 women, 1980-1988), and controls were persons with endoscopic findings negative for adenoma (9,159 men and 8,585 women). After adjustment for age, total energy, family history of colorectal cancer, body mass index, alcohol consumption, folate, intake of saturated fat and fiber, indications for endoscopy, and previous endoscopy, total calcium intake was not associated with the risk for adenoma (relative risk (RR), highest vs. lowest quintile of intake: men, 1.13, 95% confidence interval (CI) 0.76-1.66; women, 1.17, 95% CI 0.81-1.69). Total vitamin D intake was unrelated to the risk for adenoma in men (RR = 1.29, 95% CI 0.87-1.93). An inverse nonsignificant association was observed in women in the 1980-1988 analyses (RR = 0.68, 95% CI 0.41-1.13, trend p = 0.09), mainly attributable to the intake of multivitamin supplements, but an analysis of 4-year data (1984-1988) using a more detailed dietary assessment showed no association with vitamin D (RR = 1.04, 95% CI 0.65-1.67). Milk consumption and intake of total fermented dairy products were not related to adenoma risk. In conclusion, the occurrence of colorectal adenoma was neither related to calcium intake nor to milk consumption, whereas vitamin D from supplements but not diet was slightly, but not significantly, inversely associated with risk among women only.