Attrition from treatment for substance abuse disorders is a persistent challenge that severely limits the effectiveness of services. Although a large body of research has sought to identify predictors of retention, the perspective of clients of services is rarely examined. This exploratory qualitative study presents clients' stated reasons for leaving outpatient treatment (n = 135, 54% of the sample of 250) and their views of what could have been done differently to keep them engaged in services. Obstacles to retention fell into program- and individual-level factors. Program-level barriers include dissatisfaction with the program, especially counselors; unmet social services needs; and lack of flexibility in scheduling. Individual-level barriers to retention were low problem recognition and substance use. Study limitations are noted, and the implications of findings for research and practice are discussed, emphasizing the need to understand and address clients' needs and expectations starting at intake to maximize treatment retention and the likelihood of positive outcomes.