Objective: Delirium is an acute onset syndrome characterised by disturbances of consciousness, attention, cognition and perception (O’Malley, Leonard, Meagher and O’Keefe, 2008). Previous studies have examined the risk factors and aetiology connected with delirium but research to date has failed to systematically investigate attentional deficits presented in patients with delirium. The aim of the present study was to investigate the attentional deficits in delirium and compare with Alzheimer’s dementia (AD) and cognitively unimpaired participants. Methods: Cognitive and attentional deficits were investigated in three groups from acute medical and surgical wards at the Royal Infirmary Hospital, Edinburgh and a memory clinic at the Royal Victoria Hospital, Edinburgh. Cognitive and delirium test batteries in addition to a pioneering vigilance box task were administered to 57 patients over 65 years. Results: Non-parametric data was examined using Kruskal-Wallis tests and further Man-Whitney U tests were carried out to test group differences. The delirium group showed significant attentional deficits compared with the AD and unimpaired control groups on all vigilance tasks. Furthermore, there were no significant differences found between the AD and unimpaired control groups across vigilance tasks. In addition, it appeared that as severity of delirium worsened the attentional deficits increased. Conclusions: It is concluded that attentional deficits are indeed worse in delirium than in AD, however further research is required to establish the specificity of these deficits.