AbstractObjectives:To examine the association between increasing age and extended length of hospitalisation, and the impact of an acute geriatric unit on this association.Design:Retrospective analysis of concurrently collected data of patients admitted to three general medical units, one of which was an acute geriatric unit.Setting:Alfred Hospital, Melbourne (a tertiary referral teaching hospital), between 1 July 1993 to 30 June 1994.Patients:Those classified into the same diagnosis‐related groups (DRGs) as the 15 most common DRGs of the acute geriatric unit.Outcome measure:Incidence of patients with extended lengths of stay (“high outliers”), analysed by age, medical unit and DRG.Results:Of 3499 patients discharged from the hospital with the 15 study DRGs, 303 patients (8.6%) were from the acute geriatric unit, and 274 and 300 patients (7.8% and 8.5%) were from the two other general medical units, respectively. Patients in the acute geriatric unit were significantly older (median age group, 75–79; age range, 18–98) than patients in all other hospital units (median age group, 60–64; age range, 18–97) (P<0.0001). Analysis of patients with respiratory and cardiovascular DRGs admitted to all general medical units compared with specialty units showed this age discrepancy was even more marked for patients aged over 85. There was an increased likelihood (P<0.001) of an extended length of stay for patients aged over 55. The incidence of high outliers for comparable DRGs was lower for patients cared for by the acute geriatric unit, compared with general medical units. In the acute geriatric unit, unlike the overall trend, the proportion of high outliers did not increase with age.Conclusions:The specialised management of acute geriatric medical units can counteract the trend towards increased incidence of high outliers with increasing age, despite significantly older patients.