This clinical trial employs a two-fold approach, utilizing a single-arm feasibility design within a larger multiple baseline experimental case series study framework over 32 weeks. The study aims to investigate both the feasibility and efficacy of Radically Open Dialectical Behaviour Therapy (RO-DBT) in patients with anorexia nervosa (AN). Feasibility will be assessed through treatment retention, data collection engagement, patient satisfaction, and the occurrence of adverse events. Efficacy outcomes will focus on RO-DBT's impact on ED psychopathology, obsessive-compulsive personality traits, EDR, and BMI.

Anorexia nervosa (AN) is characterized by high chronicity and mortality rates. Despite its relatively high prevalence, effective treatments remain elusive, often resulting in extended treatment durations and high dropout rates. Emotional dysregulation (EDR) and obsessive-compulsive personality traits are central to the psychopathology of AN, directly contributing to the disorder's severity and persistence. Radically Open Dialectical Behaviour Therapy (RO-DBT) targets the psychopathology mentioned above and has shown promise in pilot studies with AN patients.

Given the urgent need for effective AN treatments and the potential of RO-DBT, this study aims to investigate both the feasibility and efficacy of this therapy in a clinical setting. The study will employ a single-arm feasibility design within a multiple baseline experimental case series framework over 32 weeks, involving 31 patients aged 16 years and older diagnosed with typical or atypical AN. All assessments will utilize validated psychometric instruments, and trained psychotherapists will administer RO-DBT.

Feasibility will be assessed through:

• Treatment retention
• Data collection engagement
• Patient satisfaction with treatment
• Occurrence of adverse events.

The primary efficacy outcome this trial aims to investigate is:

* Does RO-DBT reduce eating disorder psychopathology in AN as measured by the Eating Disorder Examination Questionnaire (EDE-Q)?

The secondary efficacy outcomes this trial aims to investigate are:

• Does RO-DBT reduce emotional dysregulation in AN as measured by change in the Expressive Suppression subscore of Emotion Regulation Questionnaire (ERQ)?
• Does RO-DBT reduce obsessive-compulsive personality traits in AN as measured by change in the total score of the Five-Factor Obsessive Compulsive Inventory (FFOCI-SF)
• Does RO-DBT increase body weight as measured by change in Body Mass Index (BMI)?

We hypothesize that RO-DBT will be a feasible treatment option for individuals with AN. Furthermore, we anticipate observing reductions in ED psychopathology and expressive suppression, alongside an increase in BMI, between pre- and post-treatment assessments.

Inclusion Criteria:

• Diagnosis of anorexia nervosa or atypical nervosa (i.e., in partial remission with a BMI above ~18.5 but meets criteria B and/or C) according to the Diagnostic and Statistical Manual fifth edition (DSM-5)
• Signed written informed consent form
• Age 16-65
• Sufficient knowledge of Swedish

Exclusion Criteria:

• Substance dependence
• Not willing to accept randomization
• Undergoing simultaneous psychotherapy via another healthcare provider
• Intellectual disability
• Any psychiatric, medical or social condition whether or not listed above, due to which, in the judgment of the investigators and after any consults if indicated, participation in the study is not in the best interest of the patient.