BACKGROUND:: Vitamin D deficiency is related to various cardiovascular diseases, including sudden cardiac arrest (SCA). This study investigated the association of vitamin D level with neurologic outcome and mortality after resuscitation from SCA. PATIENTS AND METHODS:: We enrolled patients who were successfully resuscitated from out-of-hospital cardiac arrest of presumed cardiac cause in Severance Cardiovascular Hospital as a prospective cohort registry. Baseline blood samples including pH, lactate, and vitamin D were obtained without fluid replacement just after hospital admission. Outcome was assessed by cerebral performance category (CPC) score at 1 month after SCA. Favorable outcome was defined as survival with CPC score of 1 or 2, whereas unfavorable one as death or survival with CPC scores of 3 through 5. Severe vitamin D deficiency was defined as 25(OH)D <10 ng/mL. RESULTS:: A total of 163 patients were included. Overall 96 (59%) patients had a favorable neurologic outcome, whereas 67 patients (41%) showed unfavorable outcome, including 37 (23%) mortality. Patients with unfavorable outcome were likely to be female and have initial non-shockable rhythm, longer arrest time, severe shock, diabetes, and baseline renal dysfunction. In multivariate analysis, severe vitamin D deficiency was one of the poor prognostic factors of both unfavorable neurologic outcome and mortality after SCA. CONCLUSIONS:: Vitamin D deficiency is very prevalent and strongly associated with both unfavorable neurologic outcome and mortality in patients resuscitated from SCA.