Researchers at CHOP are trying to improve outcomes in the treatment of adolescents with anorexia nervosa. Eligible families will receive Family Based Treatment for anorexia nervosa. Some adolescents with anorexia nervosa will also receive Cognitive Remediation Therapy (a treatment that increases flexible thinking). Both parents are required to participate and any siblings living at home are asked to come to the first four treatment sessions. Families will receive treatment for approximately 6 months and will be asked to complete number of assessments during treatment and at two time points after treatment ends.