Vitamin D is obtained from the diet and synthesized in skin exposed to sunlight. Vitamin D status, assessed by circulating 25-hydroxyvitamin D [25(OH)D], has been associated with a reduced risk of colorectal cancer in previous studies. To complement existing evidence, we conducted a case-control study nested within the Multiethnic Cohort including men and women of Japanese, Latino, African-American, White, and Native Hawaiian ancestry. Using a direct competitive chemiluminescence immunoassay, 25(OH)D level was determined in plasma drawn before diagnosis from 229 cases and 434 controls matched to cases by area (Hawaii, Los Angeles), sex, ethnicity, birth year, blood draw date and time, and hours fasting. Odds ratios (OR) were estimated with conditional logistic regression. An inverse trend was observed (OR per doubling of 25(OH)D, 0.68; 95% confidence interval, 0.51-0.92; P = 0.01), but when examined in categories, relative to the first quintile (<16.8 ng/mL), the ORs in all other quintiles were quite similarly reduced between 37% and 46%. The association was not significantly heterogeneous among the four largest ethnic groups (P(heterogeneity) = 0.46). In summary, this study provides evidence of an association between vitamin D status and reduced risk of colorectal cancer in an ethnically diverse population.