 The aim of the research is to determine if Cognitive Behaviour Therapy CBT specific for BDD is more effective than a credible non-specific form of CBT for treating BDD and its delusional variant in adults aged 17 or over. This will be done in a single centre randomised controlled trial that compares specific CBT for BDD versus non-specific CBT over 12 weeks. The hypotheses to be tested are that: 1 specific CBT for BDD will be more effective than non-specific CBT at 12 weeks 2 Treatment effects from Specific CBT will be maintained at 1 month follow up. The main study end-point is at 12 weeks and the secondary end-point is at 1 month follow up. A secondary aim is to explore whether delusionality insight as measured by the Brown Assessment of Beliefs and co-morbid depressed mood predicts response to treatment. 