Objective: Little is known about the epidemiology of body dysmorphic disorder in youth. We evaluated the prevalence, comorbidity, and psychosocial impairment associated with BDD and more broadly defined appearance preoccupation in young people.Method: Data were drawn from the 2017 Mental Health of Children and Young People in England survey. BDD and psychiatric comorbidity were assessed in 5-19 year olds (N = 7,654) according to DSM-5 criteria, using a clinician-rated standardized diagnostic assessment. Psychosocial impairment was measured with a quantitative scale, and indexed by reported self-harm and suicide attempts, and service utilisation, assessed using structured interviews. Results: The point prevalence of BDD was 1.0% (95% CI 0.8 – 1.3%). BDD was significantly more common among adolescents than children (1.9 vs 0.1%; OR = 22.5, p<0.001), and females than males (1.8% vs 0.3%; OR = 7.3, p<.001). Similar age and sex effects were observed for appearance preoccupation. Approximately 70% of young people with BDD had psychiatric comorbidity, most commonly internalizing disorders. BDD was associated with self- and parent-reported psychosocial impairment, self-harm and suicide attempts, and service utilisation. Appearance preoccupation was more common than full-syndrome BDD, but showed similar age and sex effects, patterns of comorbidity, and associated impairment. Conclusion: BDD and appearance preoccupation are relatively common, especially among adolescent girls, and associated with substantial co-occurring psychopathology, risk, and impairment. Improved screening is needed to increase detection and diagnosis of BDD, and to facilitate access to evidence-based treatment. Future research should seek to establish whether appearance preoccupation as a target for early intervention.