Background:Hoarding disorder (HD) is a new diagnosis inDSM-5 (American Psychiatric Association, 2013). Cognitive-behavioral therapy (CBT) appears promising for the treatment ofHD, and has been tested in both individual and group settings.Methods:The present study used meta-analytic techniquesto examine the overall strength of effect of CBT on HD, aswell as on its component symptoms (clutter, difficulty dis-carding, and acquiring) and associated functional impairment.Potential demographic and treatment-related moderators ofCBT response, as well as the presence of clinically significantchange were also examined. From 114 published articles, 10articles comprising 12 distinct HD samples (N5232) metinclusion criteria and were retained for analysis.Results:HD symptom severity decreased significantlyacross studies with a large effect size. The strongesteffects were seen for difficulty discarding, followed byclutter and acquiring. Functional impairment showed thesmallest effect in the moderate range. Female gender,younger age, a greater number of CBT sessions, and agreater number of home visits were associated with betterclinical outcomes. Reliable change was found in themajority of samples for each outcome domain. Rates ofclinically significant change, however, were lower (per-centage ranged from 24 to 43). Thus, in most cases, studypatients’post-treatment scores remained closer to theHD range than to the normal range.Conclusions:CBT is a promising treatment for HD,although there is significant room for improvement.Results are discussed in terms oftreatment refinement forHD, and additional moderator variables are suggested forfurther study. Depression and Anxiety 32:158-166, 2015.Focus 2021; 19:468–476; doi: 10.1176/appi.focus.19403Reprinted with permission from Wiley(Appeared originally in Depression and Anxiety 2015; 32:158–166)