This retrospective study explores depression, worry, psychosocial functioning, and change in body mass index (BMI) as predictors of eating disorder (ED) symptomatology and BMI at discharge and 1-year follow-up from a residential and partial hospitalization ED treatment center. Participants were 423 male and female patients receiving treatment at an ED treatment center. Results indicate significant improvement in ED symptomatology, psychological impairment, and change in BMI (in patients with anorexia nervosa) at treatment discharge and follow-up compared to treatment admission (ps < 0.001). Depression and worry predicted ED symptomatology and psychological impairment at discharge (ps < 0.05). Depression, worry, and psychosocial functioning predicted ED symptomatology and psychological impairment at 1-year follow-up (ps < 0.001). Change in BMI was not a significant predictor of outcome. Depression, worry, and psychosocial functioning each play a role in treatment outcomes and may help clarify who might benefit from treatment. Clinicians in ED treatment centers should consider these as areas of focus for improved outcomes.