The aim of the present research is to verify the immune status against tetanus in students and workers exposed to risk and to ascertain whether a decennial booster is necessary. Antibodies against tetanus were measured in 1433 workers and students of Padua University (Italy). The enrolment criterion was the ability to provide a booklet of vaccinations released by a public health office. The influence of age, gender, the number of vaccine doses, and the interval since the last dose was determined. Ten years after the last dose, the majority of subjects (95·0%) displayed an antibody titre above the protective level (⩾0·10 IU/ml), and half of these (49·1%) had a long-term protective level (⩾1·0 IU/ml). According to our data, titre depends on both the number of vaccine doses and the interval since the last dose (P < 0·0001). Five vaccine doses and an interval of at least 10 years since the last dose are predictive of a long-term protective titre in absence of a booster (1·97 IU/ml). These data suggest that when primary series are completed, a decennial booster is unnecessary for up to 20 years. Furthermore, we recommend measuring the antibody level before a new booster is given to prevent problems related to over-immunisation.