Hepatitis B surface antigen-positive allografts may be a source of transmission in patients who undergo renal transplantation. Treatment of hepatitis B virus infection with nucleoside/nucleotide analogs in kidney recipients who have hepatitis B virus infection or who have received transplants from hepatitis B surface antigen-positive donors improves long-term patient survival. Antiviral agents are administered as a preemptive or prophylactic therapy at the time of kidney transplantation, rather than as salvage treatment. In this report, we present 2 renal transplant recipients who had hepatitis B virus reinfection or who had developed seroconversion with immunosuppressive treatment. These case reports also demonstrate the unexpectedly different courses of hepatitis B reinfection after kidney transplantation.