The purpose of this study was to compare the incidence of functional deterioration of elderly patients hospitalized in acute care geriatric units compared to that in a conventional care unit. We performed a prospective controlled study over 9 months of patients above 65 years old with acute medical pathology. Upon discharge, we compared the degree of functional deterioration using the Katz index compared to the basal level before admission of both groups. Of the 143 patients studied, 68 were admitted to the geriatric care unit and 75 to the conventional care unit. In the geriatric unit, the incidence of functional deterioration occurred in 13 patients (19.1%), while in the conventional care unit it occurred in 30 (40%) (p=0.01). In a multivariate analysis of logistical regression, the odds ratio of developing functional deterioration at discharge in the conventional care unit, compared to the geriatric unit was 4.24 (95% CI: 1.50-11.99). The length of stay was shorter in the geriatric unit (7.5 vs. 9.92, p=0.03). We conclude that the elderly patients admitted to a geriatric care unit showed less functional deterioration on discharge compared with those kept in another care unit of a conventional type.