BACKGROUND:: The traditional acute care for the elderly (ACE) unit has demonstrated improved functional outcomes without increased costs or changes in length of stay (LOS). It is, however, limited in scope to patients cared for on a fixed geographical unit. OBJECTIVE:: To compare operational and quality outcomes for patients cared for on a mobile ACE (MACE) service to those cared for on a unit-based ACE service and matched controls on other general medical services. DESIGN:: Retrospective cohort study with propensity-score matching. SETTING:: An urban academic medical center. PATIENTS:: A total of 8094 hospitalized adults >64 years old admitted to an ACE, MACE, and general medical services from July 2006 to June 2009. INTERVENTION:: An interdisciplinary MACE service com- posed of a geriatrician-hospitalist, fellow, nurse coordinator, and social worker. MEASUREMENTS:: LOS, total cost, 7- and 30-day readmission rates, and in-hospital mortality. RESULTS:: Mean LOS and total cost were significantly lower for patients in the MACE service compared with the ACE unit service (5.8 vs 7.9 days, P < 0.001, and $10,315 vs $13,187, P = 0.002) and compared with propensity-score matched controls during the second year of operation (5.6 vs 7.2 days, P < 0.001, and $10,693 vs $15,636, P < 0.001). In-hospital mortality and 7- and 30-day readmission rates were similar in all groups. CONCLUSIONS:: A mobile ACE service may result in reduced LOS and lower costs with no change in in-hospital mortality or 7- or 30-day readmission rates when compared with standard medical service and a traditional unit-based ACE service.