What do clinicians choose to do in routine clinical practice when confronted with patients who have common comorbidities such as anxiety and depression which are of equal severity? The answer is not known for certain due to the lack of data on this vital clinical question. The indications are that the majority of clinicians in routine clinical practice, such as the UK’s Improving Access to Psychological Therapies (IAPT) services, do not use disorder-specific interventions designated as efficacious but instead prioritise clinical judgement to provide an ‘eclectic’ approach [15] [16] [17].In summary, there is very little information on the best way to address co-occurring anxiety and depression in routine clinical settings. The aim of this study was to compare the clinical outcome of CBT delivered in a routine clinical setting (an IAPT service) on depression and anxiety when CBT focused on one of these disorders vs CBT that focused on both anxiety and depression. In the process of conducting the study, it quickly became apparent that insufficient numbers of therapists had focused on CBT addressing anxiety alone to allow a valid compari- son of the approaches; the present study was therefore only able to compare CBT focused on depression alone (CBT-D) with CBT focused on both anxiety and depression (CBT-DA). CBT-D was defined as CBT which only included components of Beck’s CBT for depression protocol (e.g. cognitive restructuring and behavioural activation; [18] [19] whereas CBT-DA included components of both Beck’s CBT for depression protocol and techniques from Dugas’ treatment of anxiety disorders such as tolerating uncertainty [20] [21].Based primarily on the studies of Craske et al. [11] and [12], it was hypothesised that patients with clinical levels of anxiety and depression who received CBT focused only on depression would have a better clinical outcome for both depression and anxiety than those receiving two interventions.