Supervised Injection Facilities (SIFs) for the medical supervision of illicit drug use exist in Europe, Canada, and Australia to reduce infectious disease transmission, overdose deaths, and other harms of drug use. They have been shown to reduce rates of needle sharing by 69% and local overdose mortality by 35% without increasing rates of drug use or related crime. In light of increasing rates of illicit opioid use and overdose death in Massachusetts, the Massachusetts Medical Society recently endorsed opening a SIF in Boston. This thesis proposes a study of the Boston SIF with the hypothesis that higher SIF utilization will be associated with decreased incidence of fatal overdose, HIV seroconversion, and HCV seroconversion during the study period. I propose evaluating this hypothesis prospectively by following clients of the SIF at 6 month intervals and comparing the rates of overdose death and HIV or HCV seroconversion among frequent and infrequent clients of the SIF. Based on data reported from previous SIFs and projections of the population of people who inject drugs (PWID) in Boston, a study with this design should detect a significant difference in these three primary endpoints between people using the SIF frequently and those using it infrequently within five years. A positive finding would confirm the efficacy of SIFs in harm reduction and secondary prevention for Opioid Use Disorder (OUD), potentially leading to broader adoption in other hotspots of opioid use in the United States.