Many cities throughout the world are experiencing ongoing infectious disease and overdose epidemics among illicit injection drug users (IDUs). In particular, HIV and hepatitis C virus (HCV) have become endemic in many settings and bacterial infections, such as endocarditis, have become extremely common among this population. In an effort to reduce these public health concerns, in September 2003, Vancouver, Canada, opened a pilot medically supervised safer- injecting facility (SIF), where IDUs can inject pre-obtained illicit drugs under the supervision of medical staff. Before and since the facility's opening, there has been a substantial misunderstanding about the rationale for evaluating SIF as a public-health strategy. This article outlines the evidence and rationale in support of the Canadian initiative. This rationale involves limitations in conventionally applied drug-control efforts, and gaps in current public-health policies in controlling the spread of infectious diseases, and the incidence of overdose among IDUs.