This study was conducted to investigate immunity to tetanus among pregnant women with verbal histories or documentation of having been vaccinated under the current five-dose tetanus toxoid (TT) schedule. It examined sera from 176 pregnant women attending antenatal care at Muhimbili Medical Centre in Dar es Salaam, Tanzania. Tetanus antitoxin level of 0.1 IU/ml was considered protective. Our findings show that 94.9% of women had tetanus antitoxin > or = 0.1 IU/ml. Multivariate analysis revealed that time after last vaccination, TT doses received and TT vaccination status explained 7.5%, 5.7% and 2.3% of variations in tetanus antitoxin levels respectively. Pregnant women with non-protective levels of tetanus antitoxin (5.1%) pose great risks of neonatal tetanus to their newborns and are also susceptible to maternal tetanus. Proper keeping of TT vaccination records is vitally important to avoid hyper-immunisation.