The human oral microflora is diverse and is usually predominately composed of Gram-positive bacteria. It is uncommon to find Gram-negative bacilli (GNB) in healthy mouths. The incidence of infection with GNB rises in institutionalised, frail elderly subjects. There is also evidence of an association between intra-oral GNB presence and denture wearing. There have been few studies which have investigated intra-oral GNB carriage in acutely ill elderly patients. The aim of this study was to evaluate the oral flora of a group of elderly patients during an acute medical admission and to investigate any associations between the oral microflora and existing medical or oral factors. A total of 28 patients (17 females and 11 males; age: 74-93 years) on a care for the elderly ward were studied. Epidemiological data, detailed medical histories and oral examinations were undertaken. In addition, oral swabs of the palate area were taken to determine their oral flora. Twelve (43%) of the patients had GNB in their oral cavities. These patients were suffering from a variety of medical conditions and were on various drug regimes. There was a correlation between oral GNB presence and denture use. There was no association between GNB presence and denture hygiene. As oropharyngeal GNB colonisation can be associated with infections such as aspiration pneumonia, it is important in patients at risk that intra-oral organisms are identified and managed.