The benefits of cognitive-behavioral treatment for obsessive-compulsive disorder (OCD) have been evidenced by several meta-analyses. However, the differential effectiveness of behavioral and cognitive approaches has shown inconclusive results. In this paper a meta-analysis on the effectiveness of psychological treatment for OCD is presented by applying random- and mixed-effects models. The literature search enabled us to identify 19 studies published between 1980 and 2006 that fulfilled our selection criteria, giving a total of 24 independent comparisons between a treated and a control group. The effect size index was the standardized mean difference in the posttest. The effect estimates for exposure with response prevention (ERP) alone (d(+)=1.127), cognitive restructuring (CR) alone (d(+)=1.090), and ERP plus CR (d(+)=0.998) were very similar, although the effect estimate for CR alone was based on only three comparisons. Therapist-guided exposure was better than therapist-assisted self-exposure, and exposure in vivo combined with exposure in imagination was better than exposure in vivo alone. The relationships of subject, methodological and extrinsic variables with effect size were also examined, and an analysis of publication bias was carried out. Finally, the implications of the results for clinical practice and for future research in this field were discussed.