Supervised injection facilities (SIF), a harm reduction intervention, may reduce several risks of public injection drug use. The prospect of conducting a scientific, multi-site pilot project of these facilities is being explored at federal and local levels in Canada. Experiences with SIF in Europe and Australia indicate that successful outcomes for the community ultimately hinge upon the responsiveness and relevance of the facilities to the needs of their primary target group: people who inject drugs in public places. Consideration of the factors and conditions found to influence a potential user's uptake of SIF, therefore, is imperative. This study sought to assess the acceptability of SIF and to determine factors associated with willingness of injecting drug users (IDU) to use SIF in a city considering their establishment. Participants were 11 key informants and 251 publicly injecting IDU. Key informants generated the Montréal-specific SIF model subsequently presented to IDU. 76% of IDU were willing to use at least one of three proposed SIF sites. Exploratory multivariable models indicated drug-use characteristics and SIF attributes as determinants of outcome: predominant cocaine injection, history of overdose, knowing about SIF, relieving and empowering feelings toward using SIF, and comfort with disclosure of one's injecting drug use. User consultations are essential to assess relevance and plan SIF acceptable to IDU. [ABSTRACT FROM AUTHOR]