The present study examined the extent to which anxiety sensitivity (AS) at treatment entry was related to prospective treatment dropout among 182 crack/cocaine and/or heroin-dependent patients in a substance use residential treatment facility in Northeast Washington, DC. Results indicated that AS incrementally and prospectively predicted treatment dropout after controlling for the variance accounted for by demographics and other drug use variables, legal obligation to treatment (i.e., court-ordered vs. self-referred), alcohol use frequency, and depressive symptoms. Findings are discussed in relation to the role of AS in treatment dropout and substance use problems more generally.