Hepatitis B virus (HBV) reactivation has been documented in association with multiple immunotherapy regimens . These reactivations can be life-threatening and result in fulminant hepatic failure. There are currently no reports of HBV reactivation on nivolumab treatment. This is a case of a patient with known HIV infection and previous HBV workup that revealed him to be anti-hepatitis B core antibody positive, hepatitis B surface antigen negative, and HBV DNA negative. He experienced a HBV reactivation while on therapy with nivolumab for stage IIIa poorly differentiated carcinoma of the lung, which was a recurrence from a prior surgically resected stage Ia well differentiated adenocarcinoma of the lung. He is a long-term nonprogressor in regards to his HIV and had previously had a negative HBV DNA level and had declined antiretroviral therapy until just prior to starting nivolumab. This case is also of interest as antiprogrammed death-1 receptors are involved in CD4+-related HIV control , and the effects of nivolumab in a patient who was an HIV long-term nonprogressor are unknown. There was concern that he would develop increased HIV viremia and CD4+-related immune dysfunction without antiretroviral therapy, and thus, he agreed to treatment prior to starting antineoplastic immunotherapy.