The optimal treatment for adolescents with chronic HBV infection is currently unknown. Treatment with interferon alfa, lamivudine, and adefovir dipivoxil in pediatric populations has been shown to be less than optimal. Further, the safety and efficacy of entecavir and telbivudine have not been established in patients < 16 years of age. A study evaluating TDF in adolescents (ages 12-17) was needed to assess the safety and efficacy of this agent in the treatment of chronic hepatitis B in this patient population. In addition, the study will help to further elucidate the pharmacokinetic (PK) and resistance profiles of TDF. Through their participation, study participants will help generate critical new information to help guide the most optimal treatment of chronic HBV infection in adolescents.