Delirium is a common event in geriatric hospitalized patients. A prospective study was performed in order to characterize predictors, features and outcome in an acute geriatric care unit in a general hospital in Israel. The tools used to detect delirium were the Confusion Assessment Method (CAM) and the Delirium Rating Scale (DRS), supported by clinical observation by an experienced geriatrician. Results showed an occurrence of 18%; risk factors were polypharmacy and poor nutritional status. Age, education, ethnic origin, pre-morbid cognition and ADL status did not show any statistical correlation with the occurrence of delirium. Delirious patients experienced longer hospital stays, more complications, high mortality rate, cognitive and functional decline. It is very difficult to prove the correlation between reduction of brain reserve and appearance of delirium, but as we have observed in other systems (cardiovascular, renal, etc.), it seems reasonable to presume that the same mechanism is involved in cognitive function. Our conclusions are that the diagnosis of delirium may be misleading by a psychiatric overwhelming presentation, and should be considered not as a transient event, but as a marker for cognitive and functional decline in the future, and therefore these patients should be looked after once discharged.