BACKGROUND/AIMS: A low vitamin D level has been associated with metabolic syndrome and diabetes. However, an association between a low vitamin D level and nonalcoholic fatty liver disease (NAFLD) has not yet been definitively established. This study aimed to characterize the relationship between a vitamin D level and NAFLD in Korea. METHODS: A cross-sectional study involving 6,055 health check-up subjects was conducted. NAFLD was diagnosed on the basis of typical ultrasonographic findings and a history of alcohol consumption. RESULTS: The subjects were aged 51.7±10.3 years (mean±SD) and 54.7% were female. NAFLD showed a significant inverse correlation with the vitamin D level after adjusting for age and sex [odds ratio (OR)=0.85, 95% confidence interval (CI)=0.75-0.96]. The age- and sex-adjusted prevalence of NAFLD decreased steadily with increasing vitamin D level [OR=0.74, 95% CI=0.60-0.90, lowest quintile (≤14.4 ng/mL) vs highest quintile (≥28.9 ng/mL), p for trend <0.001]. Multivariate regression analysis after adjusting for other metabolic factors revealed that NAFLD showed a significant inverse correlation with both the vitamin D level (>20 ng/mL) [OR=0.86, 95% CI=0.75-0.99] and the quintiles of the vitamin D level in a dose-dependent manner (p for trend=0.001). CONCLUSIONS: The serum level of vitamin D, even when within the normal range, was found to be inversely correlated with NAFLD in a dose-dependent manner. Vitamin D was found to be inversely correlated with NAFLD independent of known metabolic risk factors. These findings suggest that vitamin D exerts protective effects against NAFLD.