Introduction: Non-Alcoholic Fatty Liver Disease (NAFLD) is the accumulation of fat in the liver with the absence of other causes of fatty liver. The prevalence of NAFLD has doubled over the last two decades. It is now estimated to affect about 25% of the population, which is the most common liver disease in United States. NAFLD and vitamin D deficiency have been increasingly recognized as important causes of patient morbidity. There has been much interest in linking vitamin D to diseases that are mediated by inflammation such as NAFLD. Our hypothesis is that patients with NAFLD have higher risk of vitamin D deficiency. Methods: We performed a retrospective case - control study from the Nationwide Inpatient Sample (NIS, 2009) maintained by the Healthcare Cost and Utilization Project (HCUP) of the Agency for Healthcare Research and Quality (AHRQ). All hospitalizations (age > 18 years) with primary or secondary diagnosis of NAFLD (ICD 9: 571.8) were selected. We randomly selected equal number of controls without NAFLD from the database. The outcome of interest was the risk of vitamin D deficiency (ICD 9: 268.x). SAS 9.2 (SAS Institute Inc., Cary, NC, USA) was used to analyze co - variates related to vitamin D deficiency and NAFLD. Results: There were 33,217 patients with diagnosis of NAFLD. The overall prevalence of vitamin D deficiency among NAFLD patients was 1.03%. This is lower than expected, likely reflecting underdiagnoses in inpatient setting. We found that NAFLD patients were more likely to have vitamin D deficiency (OR: 3.160, 95% CI 2.546 - 3.922) compared to non-NAFLD patients. NAFLD patients were more likely to be obese, smokers, have hypertension, diabetes and dyslipidemia. Even after adjusting for age, gender, smoking status, race, obesity, hypertension, diabetes, hyperlipidemia and metabolic syndrome we found that NAFLD patients had a higher risk of vitamin D deficiency (OR: 2.218, 95% CI 1.759 - 2.797) compared to non-NAFLD patients. Conclusion: Our study shows that patients with NAFLD are at a 2.2 times higher risk of vitamin D deficiency and suggests a strong link between vitamin D deficiency and NAFLD. A recent meta-analysis showed that NAFLD patients are 1.26 times more likely to be vitamin D deficient. Although our data shows an even stronger link between the two conditions, further research is needed to determine the causality between NAFLD and vitamin D deficiency.Table 1: Odds Ratios of Vitamin D Deficiency Among Patients with NAFLDTable 2: Baseline Characteristics of Patients with Non—Alcoholic Fatty Liver Disease (NAFLD) and ControlsFigure 1