There is strong epidemiological and laboratory evidence that vitamin D may be protective against colorectal neoplasia. Therefore, we sought to assess the relationship between serum 25(OH)D levels, dietary intake of vitamin D, and colorectal adenoma recurrence in our ursodeoxycholic acid trial. A total of 568 participants were randomly selected for analysis of serum 25(OH)D levels. The range of total 25(OH)D was 5.5-66.1 ng/ml, with a median of 25.6 ng/ml. After categorizing 25(OH)D levels into tertiles based on the population distribution, the adjusted odds ratios (95% CI) for adenoma recurrence in the second and third tertiles were 0.88 (0.56-1.39) and 0.78 (0.49-1.24), respectively. The association between serum 25(OH)D and adenoma recurrence appeared to be stronger among women than men. As compared to those below the median value, women with serum 25(OH)D levels above the median had an OR (95% CI) of 0.59 (0.30-1.16); the corresponding OR (95% CI) for men was 0.95 (0.60-1.49). Analyses by dietary vitamin D intake revealed no statistically significant associations. In summary, the results of this study show a moderate, nonsignificant inverse association between serum 25(OH)D levels and reduced risk for colorectal adenoma recurrence, particularly among women.