AIMS: Injection drug users are at high risk for chronic hepatitis C virus infection (CHC). Opioid maintenance treatment (OMT) offers a unique opportunity to screen for CHC. This study proposed the hypothesis that a general practitioner (GP) with special interest in addiction medicine can achieve CHC screening rates comparable to specialized centres and aimed to investigate determinants for a successful CHC case finding in a primary care setting. DESIGN AND PARTICIPANTS: Retrospective medical record analysis of 387 patients who received opioid maintenance therapy between 1 January 2002 and 31 May 2008 in a general practice in Zurich, Switzerland. MEASUREMENTS: Successful CHC assessment was defined as performance of hepatitis C virus (HCV) serology with consecutive polymerase chain reaction-based RNA and genotype recordings. The association between screening success and patient characteristics was assessed using multiple logistic regression. findings: Median (interquartile range) age and duration of OMT of the 387 (268 males) patients was 38.5 (33.6-44.5) years and 34 (11.3-68.0) months, respectively. Fourteen patients (3.6%) denied HCV testing and informed consent about screening was missing in 13 patients (3.4%). In 327 of 360 patients (90.8%) with informed consent a successful CHC assessment has been performed. Screening for HCV antibodies was positive in 136 cases (41.6%) and in 86 of them (63.2%) a CHC was present. The duration of OMT was an independent determinant of a successful CHC assessment. CONCLUSIONS: In addicted patients a high CHC assessment rate in a primary care setting in Switzerland is feasible and opioid substitution provides an optimal framework.