This meta-analysis quantitatively synthesizes previous research on the relation between patient adult attachment style and patient-rated therapeutic alliance. Attachment theory predicts that past relationship experiences affect current attitudes towards and behavior in relationships, so it was hypothesized that adult attachment style would correlate with the alliance, which is an operationalization of the patient-therapist relationship. Both attachment avoidance and attachment anxiety were predicted to correlate negatively with the alliance, with avoidance predicted to have a stronger inverse relation with alliance quality. A random-effects model was used to calculate the mean weighted product-moment correlation (r) for 18 studies (nine published and nine unpublished) of individual outpatient therapy with adults. The first hypothesis was supported: the mean weighted r for avoidance and alliance was -.190 (95% confidence interval from -.257 to -.124), and the mean weighted r for anxiety and alliance was -.147 (95% confidence interval from -.211 to -.082). Implications for theory, practice, and future research are discussed.