PURPOSE: Infantile hypertrophic pyloric stenosis (IHPS) is a common surgical emergency of infants that exhibits clearly unique characteristic symptoms, but its etiology and pathogenesis are still obscure. The Fredet-Ramstedt pyloromyotomy has gained worldwide acceptance. The advantages of this operation are immediate solution of the problem and few complication. Cosmetically circumumbilical incision or laparoscopic pyloromytomy can be used. METHODS: Forty cases of IHPS admitted to the Chuncheon Sacred Heart Hospital from Jan 1997. to Dec 2002 were reviewed retrospectively. These cases underwent Fredet-Ramstedt's operation. RESULTS: The most prevalent age group was 21~30 days (10 cases: 25%), mean age was 41.4+/-9.9 days, and the males to females ratio was 4.7: 1. Among the 40 cases, 24 (60%) involved the first baby. The mean gestation age was 39.9+/-1.7 weeks and mean birth weight was 3.3+/-0.5 Kg. The mean duration of symptom was 4.1+/-1.6 days. The common symptoms were non-bile stained, projectile vomiting in all cases, an olive-shaped mass in the right upper quadrant abdomen in 21 cases (52.5%), visible peristalsis on epigastrium in 16 cases (40%), and jaundice in 1 case (2.5%). Hypokalemic alkalosis was observed in 3 cases (7.5%). The mean length and thickness of the stenotic canal, as measured in the operation, were 28.8+/-8.5 mm and 4.9+/-0.6 mm, respectively. Postoperative complications were one case each (2.5%) pneumonia, wound seroma, and recurrence. Conclusion: Fredet-Ramstedt's pyloromyotomy for IHPS is an effective operation after the correction of dehydration and electrolyte imbalance.