The efficacy of family-based treatment (FBT) in outpatient settings has led to efforts to incorporate FBT principles into higher levels of care. The present study examined predictors of improvement in an FBT-based partial hospitalization program/intensive outpatient program (PHP/IOP) as measured by the Eating Disorder Examination-Questionnaire. Participants were 113 patients with anorexia nervosa (AN) or eating disorder not otherwise specified (EDNOS) consecutively participating in an FBT-based PHP/IOP. Multilevel modeling was used to investigate predictors for adolescents and young adults separately. Predictors considered included illness duration, previous hospitalization, hospitalization immediately prior to treatment, previous outpatient therapy, hospitalization during treatment, diagnosis, gaining 4 pounds in 4 weeks, and family status as time-invariant variables. Time-varying variables considered included depression symptoms and mothers'/fathers' ratings of parental self-efficacy and expressed emotion. For adolescents, depression by time and diagnosis by time interactions were statistically significant. At all levels of depression, adolescent patients with AN demonstrated greater reductions in eating disorder symptoms compared to patients with EDNOS. For young adults, depression and gaining 4 pounds in 4 weeks were significant predictors. The relationships for young adults were curvilinear such that, while lower eating disorder symptoms were found during treatment, these gains were not maintained at follow up.