We report a patient with chronic active hepatitis C developing acute anosmia during interferon (IFN) therapy. On July 31, he began receiving 6 MU of IFN-alpha daily. On September 26, he failed to smell gas leaking from a gas cooker, so IFN therapy was discontinued. He showed no reaction on a standard olfactory acuity test. As the patient had borderline diabetes, the association of anosmia with impaired glucose tolerance cannot completely be excluded, but his anosmia was probably induced by IFN therapy, since anosmia developed 10 days after the initiation of the IFN therapy, without any deterioration of his glucose intolerance.