Epidemiology: Incidence of 3/1000 births. 4 times more in males. Aetiology is unknown. In some cases there seems to be a familial association. In such families the mother has suffered from the condition in 50 per cent of cases. Characteristically it is a first-born male child that is most commonly affected. The condition is most commonly seen at 4 weeks after birth ranging from the third week to, on rare occasions, the seventh. Inexplicably, it is the time following birth that seems important and not the child’s gestational age. A premature infant will also develop the condition at about 4 weeks after birth. Pathology: Grossly hypertrophied musculature of the pylorus and adjacent antrum, the hypertrophy being maximum in the pylorus itself. The mucosa is compressed such that only a probe can be inserted. Clinical features : Vomiting is the presenting symptom that after 2—3 days becomes forcible and projectile. The child vomits milk and no bile is p...