Individuals with resolved hepatitis B, characterized as hepatitis B surface antigen (HBsAg)-negative and hepatitis B core antibody-positive, have latent hepatitis B virus (HBV) infection in their liver tissue. Cytotoxic chemotherapy and hematopoietic stem cell transplantation sometimes trigger the reactivation of latently infected HBV, resulting in de novo hepatitis B. Although de novo hepatitis B could cause acute liver failure or chronic hepatitis, an effective management strategy for de novo hepatitis B has not been well established. Risk factors and effective management for de novo hepatitis B will be clarified.