A 7-year-old boy with hepatic hydatid cysts developed fatal hypernatraemia after surgery for cyst removal where 20% hypertonic saline (HS) was used as a scolicidal agent. Symptoms of generalised seizures, tachycardia, and hypotension developed within 6 h of surgery. Serum electrolytes confirmed hypernatraemia (170 mmol/l) and hyperchloraemia (141 mmol/l). Despite attempts at resuscitation, he died 20 h later. The literature is reviewed, emphasising the potential dangers of the use of HS and the clinical presentation and appropriate management of hypernatraemia.