Hepatitis B vaccination programs have prevented infection in many dialysis patients, although the antibody response to vaccination is still insufficient in approximately 50%. Reinfection or reactivation of latent hepatitis B infection (HBV) has been reported in certain groups of immunosuppressed patients, including those infected with the human immunodeficiency virus (HIV-1). We report the reactivation or reinfection of HBV with resurgence of hepatitis B surface antigen in a dialysis patient coinfected with HIV-1. Thus, in dialysis patients with latent HBV infection, with undetectable hepatitis B surface antigen (HBsAg) levels, the potential exists to reactivate during immunosuppression associated with HIV-1 infection and/or end-stage renal disease. Reinfection with a different subtype is also possible. The development of hepatitis B surface antigenemia in this patient population creates a potential for transmission in the dialysis setting. This is of special concern since the number of patients infected with HIV-1 and with evidence of prior hepatitis B infection is increasing in urban units.