Much has been written about the applicability of cognitive–behavioral group treatments for anxiety disorders using a transdiagnostic model. These studies generally support the efficacy of such treatments, although concern is apparent regarding the impact on therapeutic processes by including individuals with different DSM–IV anxiety disorder diagnoses within the same group. In particular, little is known about how a diagnostically heterogeneous format might impact group cohesion, treatment credibility, or therapeutic alliance. The current study examined treatment process variables from a sample of 54 individuals with an anxiety disorder diagnosis who participated in an open trial of a transdiagnostic anxiety treatment. Results replicated positive efficacy results presented elsewhere and suggested strong and increasing therapist therapeutic alliance and group cohesion throughout treatment. Furthermore, alliance and cohesion were generally related to better outcomes. Consequently, there appears to be little or no negative therapeutic impact of recruiting diagnostically heterogeneous groups in transdiagnostic treatments for anxiety.