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Objective: To understand the etiologic reasons of heroin addiction will make an important contribution to the prevention and treatment of this disease. It is thought that DRD2 TaqIA gene polymorphism affects the reward system by causing hyperdopaminergic activity and thereby might also lead to the development of substance addiction. The purpose of this study is to examine the possible relation between TaqIA polymorphism and heroin addiction. Methods: One hundred patients, who applied to Ankara Numune Hospital Alcohol and Substance Treatment and Training Centre for treatment and were diagnosed with heroin addiction as a result of the clinical evaluation that was conducted in accordance with DSM-IV were included in this study. One hundred healthy volunteers, who accepted to participate in the study as the control group and were matched with the patient group in terms of age and gender, were involved. Results: There was no statistically significant difference between the patient and control groups in terms of A1 allele carrier. As a result of the evaluation that was performed by dividing the patient group into two groups according to A1 allele carrier, no statistically significant relation was determined between the substance-use features and A1 allele. Conclusion: DRD2 TaqIA polymorphism, which is known to be associated with reward pathways, cannot be a genetic factor that is effective on the development of heroin addiction alone and it is required to consider different genes and gene-gene interactions in broader sample groups in order to determine the genetic factors causing the addiction. [Anadolu Psikiyatri Derg 2016; 17(3.000): 181-187]