BACKGROUND: The influenza is a contagious respiratory illness caused by influenza viruses. The primary target groups recommended for annual vaccination are healthcare workers and households which have frequent contact with persons at high risk and can transmit influenza to those persons at high risk. Members of these groups should be vaccinated against the flu so that they can avoid getting infected with continuously mutating influenza viruses. We assessed healthcare workers' knowledge and attitudes regarding influenza vaccination in order to help promote the vaccination rate. METHODS: This survey was carried out in two hospitals affiliated with the Catholic University School of Medicine, from December 2004 to January 2005. Of the 3,023 questionnaires distributed, 2,023 could be evaluated. RESULTS: The most frequently cited reason for receiving influenza vaccine was self-protection against influenza (55.4%). The most common reasons for not receiving influenza vaccine are personal health problems such as concurrent flu, pregnancy or breast-feeding (29.2%). There is no significant difference in the frequency of side effect between two groups receiving and not receiving vaccine. The most frequent side effect of influenza vaccination is flu-like syndrome; People receiving vaccine have more significant knowledge than those people not receiving vaccine about efficacy of flu vaccination, risk of influenza infection of healthcare workers and their need of flu vaccination. CONCLUSION: In order to promote the vaccination rate, education targeting people at high risk need to keep continuous and facilitate access to vaccination.