This study explored the expression, occurrence, and treatment outcomes of comorbid body dysmorphic disorder (BDD) in 107 youth (7–17 years) seeking treatment for primary obsessive–compulsive disorder (OCD). In the overall sample, appearance anxiety (AA) was positively associated with OCD-related impairment, severity, symptom frequency, comorbid symptoms, and maladaptive emotion regulation. Comorbid BDD occurred in 9.35% of youth, equally affected males and females, and was associated with older age. AA negligibly reduced following treatment. Compared to those without (a) comorbid BDD and (b) without any comorbidity, youth with comorbid BDD reported greater social impairment and reduced global functioning but did not differ on the occurrence of comorbid anxiety and mood disorders. OCD response or remission rates did not differ. In youth with comorbid BDD, AA did not significantly reduce following treatment. Results suggest a more severe expression accompanies comorbid BDD in youth with OCD, with BDD persisting following OCD treatment.