Co-morbid mental health conditions are highly prevalent in autism spectrum disorders (ASD). Cognitive behaviour therapy (CBT) is frequently used to treat these symptoms. Hence, a systematic review was undertaken to synthesise published data about the effectiveness of CBT interventions for adults with ASD and psychiatric co-morbidity. Only six studies met pre-determined review inclusion criteria: two RCTs; one quasi-experimental study; one case series; and two case studies. Meta-analysis was not possible due to study heterogeneity. A narrative analysis of the data suggested that CBT interventions – including behavioural, cognitive, and mindfulness-based techniques – were moderately effective treatments for comorbid anxiety and depression symptoms, albeit that sample sizes were small, participant characteristics varied widely, and psychometric properties of self-report outcome measurements utilised in the ASD population remain subject to some debate. Several studies described adaptations to standard CBT including an increase in the number of sessions, or accommodation of core ASD characteristics and associated neuropsychological impairments within the therapy process.We suggest further empirical research is needed to (1) investigate the acceptability and effectiveness of a range of CBT interventions for adults who have ASD and co-morbidity, and (2) to identify which adaptations are requisite for optimising CBT techniques and outcomes in this population.