While unprotected sexual intercourse and the use of contaminated injection equipment account for the majority of HIV infections worldwide, other routes of HIV transmission have received less attention. We report on a case of HIV transmission attributable to illicit drug market violence involving a participant in a prospective cohort study of injection drug users. Data from a qualitative interview was used in addition to questionnaire data and nursing records to document an episode of violence which likely resulted in this individual acquiring HIV infection. The case report demonstrates that the dangers of drug market violence go beyond the immediate physical trauma associated with violent altercations to include the possibility for infectious disease transmission. The case highlights the need to consider antiretroviral post-exposure prophylaxis in cases of drug market violence presenting to the emergency room, as well strategies to reduce violence associated with street-based drug markets.