This report describes our experience with two cases of pyogenic spondylitis with chronic hepatitis C during combination therapy of interferon alfa and ribavirin. The first patient, a 59-year-old man, was treated conservatively and improved, but the second patient, a 69-year-old woman, was not improved by conservative therapy and reconstructive operation was performed. The combination therapy of interferon alfa and ribavirin has a high risk of severe infectious diseases as side effects. CT scan and MRI are recommended immediately to diagnose pyogenic spondylitis, when patients has pyrexia and lumbago with laboratory data suspected inflammation during interferon therapy.