Effective communication between clinicians is essential for the success of mental health interventions in multidisciplinary contexts. This relies on a shared understanding of concepts, diagnoses and treatments. A major assumption of clinicians when discussing psychological treatments with each other is that both parties have a shared understanding of the theory, rationale and application of the respective technique. We aimed to determine to what extent there is inter-rater agreement between clinicians in describing the content of group therapy sessions. Pairs of clinicians, drawn from a large multidisciplinary team (13), were asked to provide ratings of the therapeutic content and emphasis of N = 154 group therapy sessions conducted during an intensive residential treatment program for post-traumatic stress disorder (PTSD). In most therapeutic content domains there was a moderate level of agreement between clinicians regarding session content (Cohen's Kappa 0.4 to 0.6), suggesting that clinicians have a broad shared understanding of therapeutic content, but that there are also frequent discordant understandings. The implications of these findings on multidisciplinary team communication, patient care and clinical handovers are discussed and directions for further research are outlined.