Platelets have a central role in the pathophysiology of thrombosis. Adenosine diphosphate (ADP) plays a pivotal role as an agonist of platelet activation. Genetic polymorphisms of the P2Y12 ADP receptor might influence the activation of this receptor by ADP or the response of patients to platelet inhibitors. The present study was conducted on a total number of 80 participants, 40 patients were diagnosed with acute coronary syndrome and 40 sex and aged-matched healthy volunteers were included as controls. Platelet aggregation was assessed (before and 1 week after clopidogrel administration) and genotyping of the T744C genetic polymorphism of P2Y12 receptor gene was carried out using the restriction fragment length polymorphism polymerase chain reaction (PCR-RFLP) method. Platelet aggregation of the patients had a range of 54-183% before clopidogrel administration and had a range of 4-113% after its administration. Genotyping of the candidate gene revealed that 72.5% of the patients had a wild allele (TT), whereas 27.5% had a C allele (heterozygous CT, homozygous CC). On the contrary, 97.5% of controls had a wild allele (TT), whereas 2.5% had a C allele (heterozygous CT, homozygous CC). Our study elicited an association between the T744C polymorphism of the P2Y12 ADP receptor gene and platelet reactivity. Carrying the C allele at this position is associated with an increased platelet activation response to ADP.