The authors conclude that the case for screening is not proven: evidence of the benefits, harms and costs of a screening programme in either population is inadequate. Although the evidence presented shows that a prevalence round of screening in intravenous drug users could be cost-effective, there is too much uncertainty surrounding this to reach a definite conclusion. In particular, the evidence relies on assumptions regarding the natural history of hepatitis C and likely adherence to diagnosis and treatment that may not be valid.