Currently, ten genotypes (A-J) of hepatitis B virus (HBV) are identified based on the nucleic acid sequence heterogeneity, and these genotypes have been shown to have distinct geographic distribution. Reports of previous studies indicated that the genotype D is the predominant type among hepatitis B patients in different regions of Turkey, however there is no data for HBV genotypes to date from Mersin region. The aim of this study was to investigate the HBV genotypes by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in chronic hepatitis B patients in Mersin province (located in the Mediterranean region of Turkey). A total of 54 serum samples were obtained from the chronic hepatitis B patients (33 male, 21 female; mean age: 40.05 years) followed-up at Gastroenterology Clinic of Mersin University Hospital. Patients had detectable HBV-DNA levels in their serum samples, and they were under antiviral therapy for at least one year. Genotyping of HBV was performed by RFLP analysis with the use of AvaII and MboI restriction enzymes after amplification of pre-S gene region by PCR. Confirmation of selected 18 cases was carried out with direct DNA sequencing. The genotypes were determined by phylogenetic comparison with 43 reference NCBI (National Center for Biotechnology Information) HBV sequences. Genotype determination was not successful in seven cases; since three of them were negative in preS-PCR, three of them yielded non-specific bands, and one of them exhibited a deleted PCR product, at the 300 bp level that was shorter than expected. Four different restriction patterns were determined in PCR-RFLP analysis of the remaining 47 samples. One of these patterns which was AvaII [-]/MboI [306/89/51], was clearly discriminated in 72.3% (34/47) of the samples as genotype D. Genotype discrimination of three patterns could not be done properly and these patterns were AvaII [- ]/MboI [357/306/89/51] (7/47, 14.9%), AvaII [300/146]/MboI [306/89/51] (5/47, 10.7%), and AvaII [- ]/MboI [357/89/---] (1/47, 2.1%). Phylogenetic comparison of HBV sequences demonstrated that all patterns in our cases were clustered in NCBI genotype D sequences. Patterns of AvaII [300/146]/MboI [306/89/51] and AvaII [-]/ MboI [357/89/---] and deleted sample were recognized as pre-S gene variants of HBV isolates. Our data indicated that the predominant HBV type was genotype D as commonly seen in Turkey and other Mediterranean countries. The results of this study also showed that the genotype uniformity and pre-S gene variants within the HBV isolates could be crucial in terms of understanding the molecular epidemiology of HBV circulating in the Mediterranean region of Turkey.