We report on a patient with chronic hepatitis C who developed acute hepatitis B during interferon alpha treatment. However, our patient promptly eliminated HBsAg and had a sustained complete response to interferon, even 6 months after the end of treatment. Acute hepatitis B superinfection in patients with chronic hepatitis C is a rarely observed event. The natural course of these patients is unknown. In our case it may be speculated that alpha-interferon treatment contributed to the prompt elimination of HBsAg from the serum.