OBJECTIVE:To determine the level of exposure to medical and surgical procedures among Australian-born patients whose mode of acquisition of the hepatitis C virus (HCV) is unknown. METHOD:Place and time of study: Melbourne, Australia, 1998-2000. DESIGN:Retrospective case series. INSTRUMENT:Structured questionnaire administered by one interviewer. SETTING:Referral centre for hepatitis C in a tertiary teaching hospital. PARTICIPANTS:Australian-born individuals persistently HCV antibody (anti-HCV) positive on at least two second-generation commercial assays. MAIN OUTCOME MEASURES:Demographic and self-reported exposure data. RESULTS:Of 135 anti-HCV positive individuals with no known mode of transmission, 54 (40%) individuals fulfilled all the entry criteria and agreed to participate. Of the 54 cases, 53 had at least one medical/surgical procedure and/or invasive dental work; 46 (85%) had dental extractions, 19 (35.2%) had complex dental work, e.g. root canal, 44 (82%) had an operation requiring general anaesthesia, 41 (75.9%) had a procedure requiring local anaesthetic, and a number of endoscopic procedures were reported: gastroscopy (n=3), colonoscopy (n=3), laparoscopy (n=4), arthroscopy (n=5), cystoscopy (n=2). CONCLUSION:We have documented exposure to medica/surgical procedures among HCV patients with no previously recognised mode of transmission. IMPLICATIONS:The findings of this study have important public health implications for current cleaning, disinfection and sterilisation procedures and protocols (or lack of these) as well as for the policies and guidelines relating to the re-use of medical equipment such as multi-dose vials, suturing material and anaesthetic circuits.