AbstractIntroduction: Up to 80% of patients who suffer from schizophrenia have sleep impairments, which affect physical and mental health, as well as quality of life. Several tandem repeat polymorphisms (VNTRs) in the Period 3 (Per3) gene have been associated with heritable sleep and circadian variables. The purpose of this study is to investigate the relationship between the VNTR variant of the PER3 gene and genetic predisposition of schizophrenia in a Turkish population. Method: Blood samples were taken from 100 patients with schizophrenia, and from 100 normal controls who are age and sex-matched. PER3 genotyping was performed on DNA by polymerase chain reaction (PCR) using specific primers. Results: For the PER3 VNTR polymorphism, we found no significant differences in the genotype distribution and allele frequency, between the schizophrenia and control groups. No association was noted between clinical and demographical characteristics of schizophrenia patients and the PER3 VNTR genotype distribution. Conclusions: This is the first study investigating association of the PER3 VNTR polymorphism with schizophrenia in a Turkish population. In conclusion, the results of this study do not support an association between the PER3 VNTR polymorphism and risk of schizophrenia in a Turkish population.