Tetanus can be only prevented by vaccination because immunity against this disease is rarely acquired, even by natural infections. To maintain long-term protective immunity against tetanus, booster immunization is essential for adolescents and adults. Most hospitalized cases and virtually all deaths occur in people over 60 years of age. The purpose of this study was to investigate the degree of protective tetanus immunity among 50 years of age and older people in Kashan city, Iran. This cross-sectional study carried out on 180 randomly individuals aged 50 years or older who were visiting a central laboratory for health examinations in 2008. Participantsʹ serum levels of tetanus antitoxin were measured by enzyme linked immunosorbent assay. A standard questionnaire was used to collect demographic data and information about risk factors. The prevalence of protective tetanus immunity in various age groups was described and sociodemographic factors that potentially influenced the degree of tetanus immunity were analyzed. Overall, 180 persons were included. Of these, 72 (40%) had never received a toxoid booster, while 47 (26.1%) had received a booster at least once. Among all participants, 30 (16.7%) had protective tetanus antitoxin levels (≥ 0.11 IU/mL), and 34 (18.9%) had protective antitoxin levels without the need of an immediate booster ≥0.51 IU/mL. Among 86 participants aged >60 years, 6 (7%) had protective antitoxin levels ≥0.1-1 IU/mL, and 5(5.8%) had protective antitoxin levels ≥1 IU/mL. Male gender and prior receipt of toxoid booster(s) were associated with protective tetanus immunity. Tetanus antitoxin levels declined with age. It appears that most 50 years of age and older adults do not have protective levels of tetanus antitoxin because of inadequate vaccination coverage. There is a need to improve the immunity levels of this age group. It is recommended to vaccinate elderly people against tetanus.