Objectives. The goal of this research is to determine whether there is a connection between CLOCK polymorphism and myocardial infarction. Study design. Case-control study. Participants and methods. In this study, three polymorphisms of the CLOCK gene were analyzed in a group of patients with myocardial infarction and control group. In the first group there were 200 patients with myocardial infarction (114 males and 86 females) treated at Clinical Hospital Center Osijek, and in the second group there were 200 subjects who haven’t had an infarction (103 males and 97 women). The second group was recruited by a family physician. All respondents were genotyped for three polymorphisms of the CLOCK gene (rs11932595, rs6811520 and rs13124436). Results. The results of the study showed that there was a certain association between CLOCK polymorphism and myocardial infarction. Correlation was found between the rs6811520 polymorphism and myocardial infarction while the results for polymorphisms rs11932595 and rs13124436 were insignificant. Difference between patients with myocardial infarction and those in the control group was found for haplotype GTG in CLOCK gene. Statistically significant association was obtained for the polymorphism rs11932595 of CLOCK gene in patients with a history of heart attack and dyslipidemia. Conclusion. From these results it can be concluded that the polymorphism of CLOCK gene has a role in the occurrence of myocardial infarction.