Aim: The goal of this study was to determine, for the first time in an east European country, the relationship of 25-hydroxyvitamin D (25(OH)D) serum concentration with extent of coronary artery disease and prognosis in patients with acute coronary syndrome (ACS) during a three-year follow up period. 1-3PAtients And methods: The study included 60 ACS patients hospitalized at cardiology department for ACS between March 2012 and September 2012; and 60 matched controls without ACS. Standard laboratory testing and vitamin D determination were performed in all study patients. In addition, ACS patients underwent coronary angiography and were followed-up for 36 months of ACS for major adverse cardiac events (MACE). ConClusion: There is an association between low serum concentration of 25(OH)D and ACS. Vitamin D level is considerably influenced by diabetes comorbidity. There was no significant association between 25(OH)D and MACE at 36 months in ACS patients.