The investigators are trying to learn the most effective way to treat an adolescent's eating disorder and how best to involve the parents or caregivers in this process.

Typically, parents and their child are seen together in therapy. However, this can sometimes be difficult for both the parents and the adolescent. Both parents and adolescents have different concerns and are struggling with different aspects of the eating disorder. Therefore, the treatment in this study involves the parents in treatment, but does not have therapy sessions with the parents and child together.

The purpose of this study is to develop this investigational type of treatment (separated family treatment), and see what works best for adolescents and their families.

Participants meet with a therapist for 20 sessions over the course of 24 weeks. For the first 16 weeks families separate therapy sessions weekly. For the last 8 weeks families meet with the therapist bi-weekly. These bi-weekly sessions are conjoint - that is, adolescents and parents will meet with the therapist together. This is to help parents and adolescents come together as a family to continue to aid the adolescent in the treatment of his/her eating disorder.

The investigators hypothesize that adolescents who receive ASFT will demonstrate improvement in eating disorder symptoms and body-mass index, that caregivers who participate in ASFT will demonstrate decreased distress and caregiver burden, that increases in psychological acceptance will be seen for both adolescents and caregivers post-treatment, and that treatment will be viewed as both credible and acceptable to both caregiver and adolescent

The purpose of this study is to develop and gather preliminary data on an acceptance-based behavioral treatment for adolescents with anorexia nervosa (AN) that is delivered in a separated family format. The treatment will combine a parent's skills curriculum that has demonstrated preliminary effectiveness in the treatment of AN, with a novel adolescent component based on Acceptance and Commitment Therapy (ACT). ACT has been found to be useful in the treatment of an array of psychological difficulties, and may be particularly well-suited for the cognitive and behavioral avoidance and rigidity that characterizes individuals with AN and their caregivers.

Inclusion Criteria:

• Adolescent is between 12-18 years of age and living in home with caregivers
• Parent or primary caregiver willing to attend therapy sessions
• Adolescent meets diagnostic criteria of anorexia nervosa (either restricting or binge/purge subtype) or subthreshold AN (relaxation of weight criterion to 90% of ideal body weight as determined by weight history and CDC growth curves) or eating disorder not otherwise specified (with restricting as the primary symptom) according to the DSM-IV TR
• Adolescent is appropriate for outpatient care and receives medical clearance from a primary care physician

Exclusion Criteria:

• Caregiver or adolescent with a co-morbid diagnosis of psychotic disorder, bi-polar disorder, or substance dependence
• Caregiver or adolescent with diagnosis of mental retardation or a pervasive developmental disorder
• Adolescent with a diagnosis of eating disorder not otherwise specified with the primary symptoms of bingeing and purging, binging without compensatory behaviors or spitting food or with restricting patterns but a BMI greater than 90% ideal weight (as determined by weight history and CDC growth curves)
• Adolescent with extreme malnutrition or other medical complications/diagnoses that require a higher level of care
• Acute suicide risk