Solitary plasmacytoma accounts for a small percentage of plasma cell neoplasms. The disease often affects older people and is potentially curable. Only a few cases of solitary jaw plasmacytoma have been described in the literature. Here we report the case of a 76-year-old woman affected by chronic hepatitis C infection and isolated plasmacytoma of the left jaw. Plasmacytoma was diagnosed in January 2001, but the swelling of the mandible had been present since 1993. Two different pathologists made the diagnosis on the basis of biopsy material from the mandibular swelling.