The authors studied 61 geropsychiatric patients with delirium from a cohort of 843 consecutive admissions to a geriatric clinical research unit. A central study goal was to assess how the presence of dementia affected the presentation of delirium. Eighteen delirious (D) and 43 delirious-demented (D-D) patients were compared on the Delirium Rating Scale (DRS), Mini-Mental State Examination (MMSE), Brief Psychiatric Rating Scale (BPRS), and EEG. D-D patients had lower MMSE scores, but no differences were found in total DRS or BPRS scores or in EEG grade. DRS items were similar in the two groups except that D-D had more cognitive impairment than D. An exploratory principal components analysis of DRS items identified two core factors. The authors conclude that the presentation of delirium in the setting of concurrent dementia is very similar to delirium without dementia, with subtle differences probably attributable to dementia.