This article reports the development of the NEECHAM Confusion Scale for rapid and unobtrusive assessment and monitoring of acute confusion. The scale was tested in two samples (N = 168 and 258, respectively) of elderly patients hospitalized for acute medical illness. Internal consistency and interrater reliability of the instrument were found to be high. The NEECHAM correlated well with the Mini-Mental State Examination and the sum of DSM-III-R positive items. Factor analyses identified and confirmed cognitive/behavioral and physiological domains. The NEECHAM provides a valid and reliable bedside assessment of acute confusion, particularly at its onset and in patients with "quiet" manifestations.