Heroin users are at high risk for HIV infection, but little is known about HIV risk in oxycodone users. This study examined HIV risk behaviors in heroin (n = 27) and oxycodone (n = 23) users seeking inpatient detoxification at a private psychiatric hospital. Drug use histories were similar, except oxycodone users used marijuana more frequently. Injection drug risk occurred exclusively among heroin users. The rates of sexual activity (66%), unprotected intercourse (69%), sex while intoxicated (74%), and sex with strangers (24%) were similar, but more oxycodone users had multiple partners (39% vs. 6%, p < .05). HIV prevention efforts should target both heroin and oxycodone users.