Internet-delivered Cognitive-behaviour Therapy for Child and Adolescent Body Dysmorphic Disorder

Inclusion Criteria: 1. A primary diagnosis of BDD, based on the diagnostic criteria of the 5th edition of the Diagnostic and Statistical Manual of Mental Disorders. Confirmed by the assessor at the inclusion assessment using a semi-structured diagnostic interview. In cases where it is challenging to rule out the presence of actual physical defects that are clearly noticeable (e.g., if the area of concern is the genitalia), we will make a referral to an appropriate service for an expert opinion. 2. A total BDD symptom severity score on the BDD-YBOCS-A ≥24. Confirmed by the assessor at the inclusion assessment. 3. Age between 12 and 17 years. Confirmed by the caregiver/parent and subsequently by the medical record. 4. A minimum of one available caregiver/parent being able to co-participate and support the child/adolescent throughout the treatment. Confirmed by the caregiver/parent at the inclusion assessment. 5. Regular access to a computer connected to the Internet and a mobile phone to receive SMS messages (one of each per family is enough). Confirmed by the caregiver/parent at the inclusion assessment. Exclusion Criteria: 1. Previous CBT for BDD for a minimum of five sessions with a qualified therapist within the 12 months prior to the inclusion assessment. Confirmed by the caregiver/parent at the telephone screening and/or the inclusion assessment and by the medical record. 2. Simultaneous psychological treatment for BDD or for any psychiatric comorbidity. Confirmed by the caregiver/parent at the telephone screening and/or the inclusion assessment and by the medical record. 3. Initiation, change of dosage or cessation of any selective serotonin reuptake inhibitors (SSRI) or antipsychotic drugs within the six weeks prior to the inclusion assessment. Confirmed by the caregiver/parent at the telephone screening and/or the inclusion assessment and by the medical record. 4. A diagnosis of organic brain disorder, intellectual disability, psychosis, bipolar disorder, eating disorder, severe depression or alcohol/substance dependence. Confirmed by the caregiver/parent at the telephone screening and/or the inclusion assessment, with supplemental information from the semi-structured diagnostic interview and by the medical record. 5. Immediate risk to self or others requiring urgent medical attention or inpatient care, such as suicidality, or repeated self-injurious behaviours. Confirmed by the caregiver/parent at the telephone screening and/or the inclusion assessment. 6. A documented suicide attempt in the last 12 months. Confirmed by the caregiver/parent at the telephone screening and/or the inclusion assessment or by documentation in the medical record. 7. Child/adolescent and caregiver/parent not able to read and communicate in Swedish. Confirmed by the caregiver/parent at the telephone screening and/or the inclusion assessment. 8. Having a close relationship to an already included participant (e.g., sibling, cousin), to avoid being randomised into two different arms, with the risk of information "leaking" between the groups. Confirmed by the caregiver/parent or assessor at the telephone screening and/or at the face-to-face or video conference inclusion assessment.