This article draws on penal epidemiological studies to analyze data from a prisoner-driven survey measuring HCV/HIV seroprevalence and risk behaviors in one Canadian male prison. Study data illuminate confounding points of potential blood exchange among injectors and noninjectors, HCV/HIV carriers and noncarriers, tested and untested prisoners, and prison and free community members. The survey finds higher HCV/HIV incidence and testing rates among injectors, and a penal population educated about high-risk practices. This study includes the first point-in-time estimate by penal injectors on the number and condition of needles/syringes, identifying an overlooked HCV conduit: the transfer of abandoned syringe components to new(er) syringes. (Published Abstract)