Our study questioned the reliability of patients' reported tetanus immunization histories. One thousand patients at an urban teaching hospital were queried regarding their tetanus immunization status. Of the 377 patients who initially asserted having had a tetanus vaccine in the last 5 years, 98 (26%) were confirmed, either by further history taking or chart review, not to have received tetanus immunization. It appears that there is a sizeable percentage of patients who falsely report their tetanus immunization status.