This article describes a recent case of ciguatera poisoning treated with intravenous mannitol. Mannitol has been used with good effect in non-controlled studies in acutely severely poisoned patients, but is not described in the treatment of chronic or milder poisoning. Our patient was a 35-year-old Niuean man who had eaten a ciguatoxic fish two weeks previously. His symptoms were not severe but were very unpleasant and restricted his ability to work. He was given a single dose of mannitol (0.66g/kg) as an intravenous infusion over two hours. His symptoms dramatically improved within 24 hours, and within a few days he felt virtually back to his former self. He experienced no side effects to the mannitol. It is suggested that intravenous mannitol may prove to be a useful treatment for mild to moderate ciguatera poisoning, and for patients who present late for treatment.