Background: It is not clear whether cognitive behavior therapy (CBT) works through changing dysfunctional thinking. Although several primary studies have examined the effects of CBT on dysfunctional thinking, no meta-analysis has yet been conducted. Method: We searched for randomized trials comparing CBT for adult depression with control groups or with other therapies and reporting outcomes on dysfunctional thinking. We calculated effect sizes for CBT versus control groups, and separately for CBT versus other psychotherapies and respectively, pharmacotherapy. Results: 26 studies totalizing 2002 patients met inclusion criteria. The quality of the studies was less than optimal. We found a moderate effect of CBT compared to control groups on dysfunctional thinking at post-test (g= 0.50; 95% CI: 0.38-0.62), with no differences between the measures used. This result was maintained at follow-up (g= 0.46; 95% CI: 0.15-0.78). There was a strong association between the effects on dysfunctional thinking and those on depression. We found no significant differences between CBT and other psychotherapies (g= 0.17; p. = 0.31), except when restrict in outcomes to the Dysfunctional Attitudes Scale (g= 0.29). There also was no difference between CBT and pharmacotherapy (g= 0.04), though this result was based on only 4 studies. Discussion: While CBT had a robust and stable effect on dysfunctional thoughts, this was not significantly different from what other psychotherapies or pharmacotherapy achieved. This result can be interpreted as confirming the primacy of cognitive change in symptom change, irrespective of how it is attained, as well as supporting the idea that dysfunctional thoughts are simply another symptom that changes subsequent to treatment.