Hepatitis B virus (HBV) is one of the important causative agents of chronic liver disease in the world. Since HBV transmission is mainly by parenteral way and sexual contact, vertical (from infected mother to newborn) and horizontal (contact with infected subjects) transmission ways play important roles. The aim of this study was to retrospectively evaluate the intrafamilial transmission risk of HBV in our region. A total of 838 subjects (age range: 1-52 years; mean age: 19.5 years) whose parents were HBsAg positive and were admitted to our outpatient clinics in 2009, have been included to the study. Of them 389 (46.4%) had HBsAg positive mothers, 404 (48.2%) had HBsAg positive fathers and 45 (5.4%) cases had both parents as HBsAg positive. The rate of chronically [corrected] infected subjects (HBsAg positive, anti-HBs negative) with HBsAg positive parents was 14.4% (121/838), the rate of non-infected susceptible subjects (HBsAg negative, anti-HBs negative) was 38.4% (322/838), and the rate of subjects who developed immunity (HBsAg negative, anti-HBs positive) was 5.3% (44/838). HBsAg positivity rate was found to be high in subjects whose mothers were HBsAg positive (25.2%; 98/389), than those whose fathers were HBsAg positive (2.5%; 10/404) and the difference was found statistically significant (p= 0.0001). Similarly the rate of HBV infection (HBsAg positive or anti-HBs positive subjects) among the offsprings whose mothers were HBsAg positive was determined to be higher (30.3%) than those whose fathers were HBsAg positive (8.2%) (p< 0.001). According to these data, the risk of HBV transmission was estimated to be three fold higher in subjects whose mothers were HBsAg positive than those whose fathers were HBsAg positive (OR= 2.96, 95% CI 2.109-4.156). In our study it was also detected that the rate of HBsAg positivity increased with age, being 10.3% (6/58) in children below 10 years old and increasing to 33% (29/88) in 11-20 years, 47% (31/66) in 21-30 years and 65% (26/40) in > 30 years age groups. There was no significant difference between consecutive age groups, however the difference between < 10 years and > 30 years age groups was found statistically significant (p= 0.0001). In addition having HBsAg positive mother or father did not affect HBV infection rate at 0-10 years age group, however, having HBsAg positive mother significantly increased the infection rate more than HBsAg positive father in 11-20 years and over 21 years age groups (p= 0.001 and p= 0.0001, respectively). In conclusion, the transmission rate of HBV infection among the family members was found high in our region and especially mothers played an important role for the transmission of the virus to their offsprings.