A 35-year-old, 47 kg female presented for elective laparatomy, adhesiolysis and ileostomy formation. Pre-existing neurological problems precluded placement of an epidural and IV PCA was used for postoperative analgesia. A patient request for pethidine was allowed. Twenty-three hours postoperatively, a brief generalized seizure occurred without adverse sequelae. This had been immediately preceded by myoclonic-type jerking. The cumulative pethidine dose was 3,000 mg and the norpethidine level was 1.8 micrograms.ml-1. Avoidance of pethidine for IV PCA where large cumulative doses are anticipated is advised. Seizures associated with pethidine/norpethidine toxicity can occur early during pethidine usage, and there is considerable variation in measured norpethidine levels.