Hepatitis B virus (HBV) genotypes vary depending on the geographical region. The HBV genotype determined in Turkey has been genotype D which is found as the homogenously disseminated single genotype The aim of this study was to determine HBV genotypes in a group of HBV infected patients who were admitted to a university hospital in Ankara, Turkey Serum samples from HBsAg positive and anti-HBs negative 84 (52 male, 32 female) patients with HBV infection were included into the study. Anti-HBc was positive in 95 2%, HBeAg was positive in 47.6% and anti-HBe was positive in 11 9% of the patients. Mean HBV-DNA levels of the patients were 5.7 x 10(7) +/- 4 6 x 10(7) IU/ml, mean ALT levels were 131 +/- 171 IU/ml and mean AST levels were 98 +/- 170 IU/ml. HBV-DNA was extracted from serum by the phenol-chloroform method and PCR was performed to amplify the S gene region of HBV-DNA Cycle sequencing of PCR products was performed by a commercial "Cy5/Cy5.5 Dye Primer Cycle Sequencing Kit" (Visible Genetics, Canada) based on dideoxy chain termination method The sequences were read and analyzed in an automated fluorescence-based DNA-sequencing system (Long-Read Tower System, Visible Genetics, Canada) The nucleotide sequences of the patient samples were compared with the previously reported sequences in gene bank for each genotype According to the comparative analysis of S-sequences of all patient samples with the published sequences of the genotypes in gene bank, all of the 84 hepatitis B strains (100%) were shown to be related to D genotypic group, subtype ayw. A phylogenetic analysis was performed and phylogenetic trees were constructed using programs in the PHYLIP phylogeny inference package The patient samples clustered within the genotypic group D According to these results, the main HBV genotype in our patients was genotype D in accordance with the previous molecular epidemiologic information on HBV in this geographic area HBV genotype determination may help to establish more rational clinical approach in the evaluation of HBV infected patients.