This is a world-wide disease, more common in Caucasians and probably on the increase. The aetiology remains very poorly understood. Presentation is between 2 and 8 weeks with vomiting, classically projectile, in an otherwise well hungry child. The diagnosis can confidently be made in most cases by a careful test feed; ultrasound and barium meal examinations are only required for difficult cases. Intravenous fluid replacement is essential prior to surgery and 24 h or longer may be required to correct acid base disturbances and enable safe general anaesthesia. Pyloromyotomy (Ramstedt's operation) remains the only satisfactory treatment, our mortality rate for this is 0.4%. Occasional vomits occur postoperatively in over half of patients but we are sceptical of the value of graded postoperative feeding regimens. There are no known long-term sequelae to surgery and this remains a most rewarding paediatric surgical condition to treat.