Most patients with drug-induced hyponatraemia are asymptomatic and the diagnosis is made incidentally following routine blood tests. Mild cases may be managed either by stopping the drug or by careful observation if the drug is considered essential. Severe hyponatremia (serum sodium levels less than 120 mmol/l) is associated with increased morbidity and mortality (confusion, convulsions, coma, congestive heart failure e.g.). We present a case of severe water intoxication with convulsion and prolonged coma, following the use of a high dose syntocinon infusion. A 22-year-old female who has intrauterine anencephalic fetus was refered to our hospital. Intravenous oxytocin was used to induce first-trimester abortion, eight hours later generalized tonic-clonic seizures occured and coma followed. Hyponatremia was found as the cause and treated by intravenous infusion of hypertonic 3% NaCl. The patient recovered and no seizure observed on follow-up. The central nervous system manifestations of acute hyponatremia may be related to cerebral edema. Drugs administration and electrolyte disturbances should be remembered as causes of coma and seizure in obstetric patients.