This paper describes a meta-analysis of 31 studies that examined the efficacy of problem solving therapy (PST). The meta-analysis, encompassing 2895 participants, showed that PST is significantly more effective than no treatment (d=1.37), treatment as usual (d=0.54), and attention placebo (d=0.54), but not significantly more effective than other bona fide treatments offered as part of a study (d=0.22). Significant moderators included whether the PST included problem-orientation training, whether homework was assigned, and whether a developer of PST helped conduct the study.