This guideline covers recognising, assessing, diagnosing and treating obsessive-compulsive disorder and body dysmorphic disorder in adults, young people and children (aged 8 years and older). It aims to improve the diagnosis and treatment of obsessive-compulsive disorder and body dysmorphic disorder. It includes recommendations on how families and carers may be able to support people with either of these conditions, and how they can get support for themselves.