Malignant hyperthermia, a life-threatening complication of anaesthesia, occurred in a 5 1/2-year-old girl undergoing dental surgery in a dental clinic. During induction, after 20 mg of succinylcholine, the anaesthetist noted a moderate rigidity of the mandible that did not interfere with the tracheal intubation. However, after 45 minutes, the temperature rose to 38.8 degrees C, pulse was rapid at 160 per minute and the child was slightly cyanosed. The diagnosis of malignant hyperthermia was made (the temperature eventually reached 40.8 degrees C). The child was immediately treated with refrigeration, procainamide and sodium bicarbonate. She was then moved to a hospital centre where the treatment was continued and she recovered completely. After extensive investigation, we found that the paternal grandfather of the child died at age 58, several hours after a bilateral lumbar sympathectomy under general anaesthesia. The cause of the death, as confirmed by hospital records, was malignant hyperthermia. No genetic counselling was given at that time; this omission has since been corrected. Early diagnosis and the availability on the premises of the necessary drugs and equipment to treat such a complication probably saved this child's life. In 1975, "La Corporation Professionnelle des Médecins du Québec" published standards for practice of anaesthesia outside a hospital setting. The compliance of the dental clinic with such standards has contributed to the avoidance of a catastrophe.