Objectives: The aim was to examine the cognitive deficits caused by delirium, with the specific goal of investigating the prevalence of cognitive perceptual deficits. To ensure this deficit is not a result of a general cognitive impairment the perceptual abilities of the delirious patients were compared against those of Alzheimer’s dementia patients. Participants: Fifty-two patients were recruited (34 female and 18 male; mean age 82.4, SD=5.4); 19 cognitively unimpaired, 19 delirious patients and 14 Alzheimer’s dementia patients. Procedure: Participants were given a battery of tests including the Mini Mental State Examination (MMSE) and a Brief Attentional Task (BAT) test, to assess general cognitive functioning and the inform the delirium measures; the Delirium Symptom Interview (DSI), the Memorial Delirium Assessment Scale (MDAS) and the Confusion Assessment Method (CAM). Participants were also tested with memory tests from The Consortium to Establish a Registry for Alzheimer’s disease (CERAD) and subtests from the Visual Object and Space Perception (VOSP) battery. Results: Cognitive perceptual deficits in delirium were identified. The delirium group performed significantly worse than the cognitively normal control group; in Position Discrimination (U=97, p=.012,), Dot Counting (U=78, p=.002), Incomplete Letters (U=43, p<.01), Shape Detection (U=58, p<.01) and Object Decision (U=78.5, p=.002) The delirium group’s performance was significantly worse than the dementia control group for two tests; Incomplete Letters (U=35, p<.01) and Shape Detection (U= 61, p=.007) Conclusions: Cognitive perceptual deficits are a feature of delirium. Delirious patients performed comparatively worse than Alzheimer’s dementia controls and cognitively normal patients in standardised tests of cognitive perceptual processing.