The epidemiology of large bowel cancer suggests an etiological role for dietary factors. Although the evidence is inconsistent, several studies have suggested an inverse association between dietary vitamin D or calcium and colorectal cancer risk. We conducted a population-based case-control study to examine the relationship between dietary vitamin D and calcium and colorectal cancer among residents of Stockholm, Sweden. Between January 1986 and March 1988, 352 cases of colon cancer and 217 cases of rectal cancer diagnosed among living persons residing in Stockholm County were identified via a cancer surveillance network established among all the hospitals in Sweden and the Stockholm Regional Cancer Registry. Controls (512) were randomly selected from a computerized population registry. Dietary intake was assessed using a quantitative food frequency questionnaire focusing on average consumption during the preceding 5 years. Supplemental intake of vitamin D and calcium was not ascertained. Logistic regression was used to calculate odds ratios (ORs) as the measure of association between the exposure of interest (vitamin D or calcium) and cancer risk. Increasing levels of dietary vitamin D were inversely associated with the risk of colorectal cancer. The association was somewhat more pronounced for cancers of the rectum [OR, 0.5; 95% confidence interval (CI), 0.3-0.9 between the highest and lowest quartiles] than for cancers of the colon (OR, 0.6; 95% CI, 0.4-1.0) after adjustment for age, sex, and total caloric and protein intake. Dietary calcium was not associated with the adjusted risk of colon (OR, 1.2; 95% CI, 0.7-2.1) or rectal cancer (OR, 1.0; 95% CI, 0.5-1.9). Further adjustments for fat and dietary fiber intake, body mass index, and physical activity had little or no effect on the results. These results suggest that dietary vitamin D may reduce the risk of large bowel cancer, particularly rectal cancer. In addition, although some of the previous data suggested a protective effect for calcium against cancers of the large bowel, we could not document such an effect.