Some latent diseases, such as immune disorders, can appear during interferon-alpha (IFN-alpha) therapy. These disorders are difficult to predict because of their low prevalence in the general population. We describe a case of pernicious anemia (PA) in a patient affected by chronic hepatitis C and macrocytosis during IFN-alpha therapy. Hemoglobin (Hb) concentration reached 7.3 g/dl. Anti-intrinsic factor (IF) antibodies were present, but not antiparietal cell antibodies (APCA). Suspension of IFN-alpha and administration of vitamin B(12) resulted in normal Hb concentrations. This case is the first instance of early PA (at the second month of IFN therapy) in a patient affected by chronic hepatitis C. The only other case of PA in a patient affected by hepatitis C virus (HCV) infection occurred during the second year of maintenance IFN therapy. We recommend that particular attention be paid to such clinical and laboratory conditions as macrocytosis in administering IFN-alpha therapy for chronic hepatitis C.