The Minneapolis and Pittsburgh Veterans Affairs Medical Centers conduct virtually identical institution-wide influenza vaccination programs that include annual educational and publicity mailings to all outpatients. Despite these efforts, 40% to 50% of high-risk outpatients at both centers fail to receive influenza vaccine each year. To assess differences between high-risk vaccine recipients and nonrecipients, a self-administered questionnaire was mailed to 500 randomly selected outpatients from each site. The questionnaire asked about risk factors, vaccination status, and knowledge and attitudes regarding influenza and "flu shots." Patient risk characteristics and vaccination rates in Minneapolis and Pittsburgh were similar with 75.6% and 76.3% reporting high-risk conditions and 65.6% and 56.1% of high-risk respondents reporting influenza vaccination, respectively. High-risk vaccine recipients and nonrecipients had similar knowledge but different attitudes about influenza and "flu shots." Using stepwise logistic regression, factors positively associated with vaccination behavior were: intention to follow physician or nurse recommendations for "flu shots" (odds ratio [OR] = 7.09); previous vaccination behavior (OR = 6.36); and physician or nurse recommendations for a "flu shot" (OR = 4.29). Factors negatively associated with vaccination behavior were difficulty in coming to the medical center (OR = 0.42) and previous side effects from the vaccine (OR = 0.19). These findings suggest areas in need of additional emphasis if influenza vaccination rates are to be improved.