Injecting drug users represent a high risk group for hepatitis C (HCV) infection. Currently, screening of this group for HCV is inconsistently implemented. We designed a HCV assessment algorithm and sought to determine the frequency with which injecting drug users completed the assessment process. Prospective study of a HCV assessment algorithm in the setting of a specialist outpatient addiction treatment clinic. Participants consisted of consecutive new attenders over a six-month period with a history of injecting. Only 21 (18%) of 119 patients reached a satisfactory endpoint of assessment. Forty-eight injectors were tested for antibody to HCV, of whom 26 (54%) tested positive. Thirteen of those with positive test results were no longer attending when the test result became available. Only four of the 19 patients who were referred, attended the on-site hepatology clinic. Thorough screening of injecting drug users for HCV within one treatment service is difficult. There is a need for explicit policies on this issue involving co-operation between primary care providers and addiction services and hepatology services.