Objective: Research indicates that cognitive therapy (CT) can be differentiated from other treatment modalities based on in-session therapist behavior. However, to our knowledge, consistency in the implementation of individual CT across clinical trials has not been tested. We compared therapist adherence to CT, as well as the therapeutic alliance, in two randomized clinical trials (RCTs) of depression treatment. Method: Data were drawn from two highly cited RCTs of CT for major depression, representing a total of three sites. Trained raters coded sessions for therapist adherence to CT and the therapeutic alliance. Results: Significant differences were obtained between sites in overall level of adherence to CT, therapist emphasis on cognitive vs behavioral strategies, and therapist focus on homework. In contrast, no significant differences emerged in the collaborative structure of CT and in the therapeutic alliance. Conclusions: Despite efforts to maximize the consistency of CT implementation (e.g., via the use of the same treatment manuals, delivered by carefully-selected and experienced therapists), differences in the implementation of CT can result. Although preliminary, these findings raise questions regarding the uniformity of CT delivery across published clinical trials, and underline the importance of assessing treatment integrity, both across clinical trials and in dissemination research. © 2013 Elsevier Ltd.