Pyloric stenosis is an acquired condition, which typically develops between 2–12 weeks of postnatal life. The infants present with nonbilious vomiting, and presentation overlaps with other causes of vomiting, particularly reflux. If unrecognized or untreated, the condition leads to worsening and protracted vomiting, typically described as “projectile”, with supervening dehydration, hypochloremic alkalosis secondary to loss of electrolytes, paradoxical aciduria in an effort to conserve sodium, and, if untreated, eventually culminates in emaciation and death. Although unrecognized and often fatal for centuries, in the twentieth century great strides were made in the recognition and surgical treatment of pyloric stenosis, a condition which has now become routinely familiar to all pediatric radiologists, pediatric surgeons and pediatricians, with uniformly excellent outcome. The epidemiology of pyloric stenosis is dependent on racial and geographic extraction, with a likely polygenic influence. Among white populations of northern European descent, the incidence of pyloric stenosis is approximately 2–5/1,000 live births. This incidence decreases by 20–30% among Caucasians in India, and even further among Black and Asian populations (0.7/1,000 live births) . The proband concordance between monozygotic twins is 0.25–0.44, and that between dizygotic twins falls to 0.05–0.10 . There is a greater than five-fold increase in incidence among first-degree relatives . Regardless of underlying cause, the phenotype is most often present in males. Affected mothers have a likelihood of pyloric stenosis in 20% of their sons and 7% of their daughters, while affected fathers have a likelihood of pyloric stenosis in 5% of their sons, and 2.5% of their daughters, with a boy:girl ratio at presentation cited between 2.5–5.5:1 .