Infantile pyloric stenosis is the most frequently encountered infant gastrointestinal obstruction in most general hospitals. Although the primary therapy for pyloric stenosis is surgical, it is essential to realize that pyloric stenosis is a medical and not a surgical emergency. Preoperative preparation is the primary factor contributing to the low perioperative complication rates and the necessity to recognize fluid and electrolyte imbalance is the key to successful anaesthetic management. Careful preoperative therapy to correct severe deficits may require several days to ensure safe anaesthesia and surgery. The anaesthetic records of 100 infants with pyloric stenosis were reviewed. Eighty-five per cent of the infants were male (i.e., 5.7:1 male to female ratio) 12% were prematures. Surgical correction was undertaken at an average age of 5.6 wk, and the average weight of the infants at the time of surgery was 4 kg. A clinical diagnosis of pyloric stenosis by history and physical examination alone was made in 73% of the infants presenting to The Hospital for Sick Children. All the infants received general anaesthesia for the surgical procedure and there were no perioperative deaths.