Obsessive-compulsive disorder (OCD) is a psychological disorder with debilitating impacts on many aspects of daily functioning, including relationships and quality of life. OCD is characterised by the presence of distressing, ongoing obsessional intrusions, and/or compulsions, which are extremely intrusive and time-consuming. There is accumulating evidence to suggest that higher-order thinking processes and beliefs (“metacognitions”) underlie many of the processes implicated in the formation and maintenance of OCD. Metacognitive models for OCD have been proposed, with debate as to whether such models are an expansion of CBT, or a separate entity. Metacognitive therapy (MCT) for OCD aims to modify the maladaptive metacognitive beliefs and processes implicated in the disorder, in order to alleviate symptoms. The current paper reports the outcomes of a preliminary trial, in which twenty-two adult outpatients with OCD received group MCT at the Anxiety Disorders Service in Canterbury (New Zealand). The results were promising, with significant decreases in OCD and depression symptoms, which were maintained at a three-month follow-up. The improvement in Yale-Brown Obsessive Compulsive Scale (Y-BOCS) scores between baseline and follow-up were large (d=1.3), comparable to the outcomes of well-established treatments. Similarly, as predicted, metacognitive beliefs were found to be correlated with OCD symptoms at baseline and follow up; and demonstrated large decreases from baseline to follow-up. Furthermore, this decrease in metacognitive beliefs throughout the study was significantly correlated with the decrease in OCD symptoms. These encouraging results add to the early empirical support for the efficacy of MCT as an OCD treatment approach, as well as reinforcing the role of metacognitions underlying this disorder. A large-scale, controlled trial is warranted, to enable firm conclusions about the efficacy of MCT and investigate the causal mechanisms of change.