AbstractClient preferences are recognized as a key component to evidence‐based practice; however, research has yet to confirm the actual influence preferences have on treatment outcome. In this meta‐analysis, we summarize results from 35 studies that have examined the preference effect with adult clients. Overall, clients who were matched to their preferred therapy conditions were less likely to drop out of therapy prematurely (OR=.59, p<.001) and showed greater improvements in treatment outcomes (d=.31, p<.001). Type of preference (role, therapist, or treatment type) was not found to moderate the preference effect, but study design was found to be a significant moderator, with randomized controlled trials showing the largest differences between preference‐matched clients and nonmatched clients. These results underscore the centrality of incorporating patient preferences when making treatment decisions. Clinical examples and therapeutic practices are provided. © 2010 Wiley Periodicals, Inc. J Clin Psychol: In Session 67:155–165, 2011.