We surveyed 306 former injection drug users receiving methadone maintenance treatment in 1997-1998 in Providence, RI regarding, (1) knowledge of hepatitis C transmission; (2) the concordance of self-knowledge of hepatitis C virus (HCV) status versus actual status; (3) perceived risk of cirrhosis; and (4) willingness to receive therapy for hepatitis C. The seroprevalence of HCV was 87%. While 77% of participants knew that HCV could be sexually transmitted, 30% did not know that condoms are protective against transmission. Thirty of 45 persons who reported they were HCV seronegative were actually seropositive; 51 of 62 persons (82%) who reported they had never been HCV tested or did not know their HCV status were serologically HCV-positive. Over half of respondents (53%) would "definitely" or "probably" use interferon therapy for viral hepatitis when informed of the risks and benefits of treatment. We found significant gaps in knowledge about HCV among IDUs. Serologic confirmation of HCV status is important among drug users, as self-report of HCV infection is often unreliable. This population, with its high prevalence of HCV, may be interested in treatments that include interferon.