A cross-sectional study was designed to evaluate the mode of transmission of HBV in household in Turkey. We also investigated the effect of the state of liver pathology of index cases on transmission. One hundred eighty index cases (122 male and 58 female with a mean age of 36.8±10.6 years) and their 380 relatives were included as the study group and 100 individuals (48 male and 52 female cases with a mean age of 41.4 ± 18.6 years) were recruited as a control group. We assayed the serological markers of HBV in participants. Biochemical tests, ultrasonography and liver biopsy were performed when necessary. The prevalence of HBs Ag positivity was 5% in spouses, 41% in siblings, 18% in children, 17% in relatives of healthy carriers, 19% in relatives of those index cases with chronic hepatitis (CH) while it was 7% in controls. HBV positivity among relatives of HBs Ag carriers and of those with CH were significantly higher than controls (p<0.05). There were more cases with liver disease among the relatives of index cases with CH (62.5%) than those of healthy carriers (29%) (p<0.05). HBs Ag carriage reaches a steady-state level of 14% until the end of second decade. Considering the rate of HBs Ag positivity (41%) among siblings of index cases, horizontal way is the most important mode for HBV transmission in Turkey. The siblings and male children are under serious risk for horizontal transmission of HBV. Unless a mass vaccination program is available, at least a vaccination program should cover first necessarily those less than 20 years of age and siblings of index cases.