A survey was made of 292 infants with congenital pyloric stenosis, diagnosed between 1967 and 1977 in seven hospitals in Israel. The incidence of the condition was estimated as 0.05 per 100 livebirths, and was higher among males, especially firstborn males. The incidence was higher among Oriental Jews than was thought, although the prevalence was higher among Ashkenazic Jews. The features of projectile vomiting, a pyloric olive and visible peristalsis were studied and their clinical and diagnostic significance was compared with that of radiological investigations. Concomitant anomalies and postoperative complications found in this series are presented. The efficacy of surgical treatment is emphasized.