In January 2005, the Department of Public Health, HSE Eastern Region, received notification of an outbreak of influenza-like illness (ILI) in a community hospital for elderly patients. Influenza A (H3N2 subtype) was isolated in 12 of 18 (66%) throat swabs sent to the National Virus Reference Laboratory (NVRL). An outbreak control team was convened. Infection control measures were put in place. Immunisation clinics were organised for non-immunised staff. The epidemic curve confirmed peak onset of illness from 14th-17th January. Attack rates were high among patients (37/74: 50%). Mortalities were also reported. A high percentage of cases occurred in patients who had been immunised (19/34: 55.6%). Seventeen of 94 healthcare workers (HCWs) became ill (18.1%), of whom only 3 (3.2%) had been immunised. A questionnaire circulated to staff identified reasons for non-immunisation. In accordance with the National Institute of Clinical Excellence (NICE) guidelines and microbiological advice, antiviral medication was recommended for patients and non-immunised HCWs as treatment or chemoprophylaxis. This outbreak highlights the importance of immunisation of HCWs against influenza.