Objective: To identify barriers to our occupational health and safety influenza vaccination program for clinical staff at the Shiraz University of Medical Science. Methods: Between November 2005 and February 2006, a random stratified sample of 884 healthcare workers (HCWs) from three university teaching hospitals were asked to complete a study questionnaire. Results: The influenza vaccine uptake rate for the current season was 5.2%. The most common reason for uptake was a belief that the nature of their work made them susceptible to influenza (73%). Reasons for not being vaccinated included: vaccine not available (35%), had little information on vaccine safety (16%), influenza is not a serious disease (14%), and immunization was not needed (13%). HCWs who believed they were at risk of influenza (mean 15.3 vs. 11.1, p = 0.007) and that the vaccine is effective against influenza (mean 16.7 vs. 12.4, p = 0.02) had significantly higher knowledge scores compared with others who did not hold these beliefs about their own vulnerability and the efficacy of the vaccine. Males were more likely than females to intend not to be vaccinated next season (OR = 2.9, p = 0.031), and those vaccinated for the current season were more likely to intend to be vaccinated next season (OR = 5.5, p = 0.002). HCWs who recommended the vaccine to family/co-workers and to their patients were also more likely (OR = 9.8, p = 0.000 and OR = 2.4, p = 0.000, respectively) to intend to be vaccinated next season. Conclusions: Convenient and free vaccination programs will increase influenza vaccination rates. To protect our HCWs and their patients, we need extensive and sustained efforts to increase HCW awareness about their vulnerability to influenza and the efficacy of the influenza vaccine. (C) 2008 International Society for Infectious Diseases. Published by Elsevier Ltd. All rights reserved.