The aim of this study was to investigate the prevalence of hepatitis B virus (HBV) genotypes in Turkey. Epidemiological and clinical data for 158 patients with acute HBV infection from 22 medical centres in the period February 2001 to February 2002 were collected prospectively. HBV genotyping was based on analysis of restriction fragment length polymorphisms and nested PCR. There were 59 female and 99 male patients, with a mean age of 34.2 +/- 15.6 years. The most common probable transmission route was blood contact in 63 (41.1%) cases, but was unknown in 78 (49.4%) cases. The mean alanine aminotransferase level was 1718 +/- 1089 IU/L. Four of the 158 patients (2.5%) died because of fulminant hepatitis. One year after discharge, 11 (10.6%) of 103 cases were positive for hepatitis B surface antigen (HBsAg) and 80 (77.7%) were positive for anti-HBsAg. Genotype determination was unsuccessful in 11 cases because of a negative PCR; genotype D was found in the remaining 147 cases. The results suggested that acute HBV infection constitutes a significant health problem in Turkey and that genotype D is predominant.