OBJECTIVE: To estimate the incremental cost of delivering intrathecal tetanus immunoglobulin compared to an intramuscular option. METHODS: To compare the two interventions, costs were estimated using standard cost methodology. Cost categories were personnel, overhead, consumables, antibiotics to treat infection, gases for respiratory assistance and immunoglobulin. Tetanus patients, aged 12 years or older, who were part of a randomised controlled clinical trial conducted in a referral hospital in Recife, Brazil, were allocated to two groups: a control group (58) and a study group (62). Patients allocated to the control group received 3000 international units (IU) of human immunoglobulin, with preservative, intramuscularly. The study group received the same quantity of immunoglobulin also intramuscularly plus an intrathecal dose of 1000 IU of a human immunoglobulin, free of preservatives, to prevent irritation of the meninges and avoid the need for corticosteroids. Thus, the difference between the two groups was the exclusive use of intrathecal immunoglobulin. The outcome measurements were clinical progression, hospital stay, respiratory assistance and respiratory infection. RESULTS: Delivering intrathecal immunoglobulin to patients saved a total of US$ 60 389, in a 10-day intensive care treatment, by preventing a worsening of their tetanus severity (e.g. from Grade I to Grades II, III, IV). Substantial cost saving was also observed in terms of hospital stay (US$ 173 104). CONCLUSIONS: Intrathecal treatment of tetanus is cost saving. This intervention deserves consideration by doctors and decision-makers as a mean of saving resources while maintaining high-quality health outcomes.