More than 10 years after the Centers for Disease Control and Prevention recommended routine HIV testing for patients in emergency departments (ED) and other clinical settings, as many as three out of four patients may not be offered testing, and those who are offered testing frequently decline. The current study examines how participant characteristics, including demographics and reported substance use, influence the efficacy of a video-based intervention designed to increase HIV testing among ED patients who initially declined tests offered by hospital staff. Data from three separate trials in a high volume New York City ED were merged to determine whether patients (N\thinspace=\thinspace560) were more likely to test post-intervention if: (1) they resembled people who appeared onscreen in terms of gender or race; or (2) they reported problem substance use. Chi Square and logistic regression analyses indicated demographic concordance did not significantly increase likelihood of accepting an HIV test. However, participants who reported problem substance use (n\thinspace=\thinspace231) were significantly more likely to test for HIV in comparison to participants who reported either no problem substance use (n\thinspace=\thinspace190) or no substance use at all (n\thinspace=\thinspace125) (x2\thinspace=\thinspace6.830, p\thinspace<\thinspace0.05). Specifically, 36.4\% of patients who reported problem substance use tested for HIV post-intervention compared to 30.5\% of patients who did not report problem substance use and 28.8\% of participants who did not report substance use at all. This may be an important finding because substance use, including heavy alcohol or cannabis use, can lead to behaviors that increase HIV risk, such as sex with multiple partners or decreased condom use.