Objective:To determine if diagnostic classification is associated with different outcomes from treatment on a geriatric assessment unit (GAU) compared with usual care for elderly patients with acute illnesses.Study Design:Reanalysis after post‐hoc diagnostic classification of a randomized clinical trial with one year follow up.Setting:Community hospital with rehabilitation facility.Subjects:A total of 155 subjects, mean age 78 years and 78% female, of whom 58 subjects had a rehabilitation classification of their diagnoses and 97 had a medical or surgical classification.Outcome Measures:Mortality, nursing home use, activities of daily living, and charges for subsequent medical services.Results:Mortality was decreased in persons with a rehabilitation classification who had received the GAU intervention. The GAU increased point‐prevalence residence in the community for persons with a rehabilitation classification. For persons with a medical‐surgical classification, the GAU intervention was associated with decreased cumulative use of nursing homes. However, GAU intervention was also associated with trends for increased charges in both diagnostic classification groups, even when adjusted for differential survival.Conclusion:Greater benefit from the GAU intervention on mortality and maintenance of residence in the community was observed in a group with a rehabilitation classification when compared with a group with a medical‐surgical classification. These improved outcomes in the rehabilitation group were not accompanied by decreased charges for later medical services that could compensate for initial rehabilitation charges.J Am Geriatr Soc 42:11