Infantile hypertrophic pyloric stenosis (HPS) is a relatively common entity. A number of studies for the postoperative feeding schedule has been studied to allow for earlier hospital discharge and improve cost-effectiveness in the treatment of HPS. The purpose of this study was to compare 3 feeding-methods and to evaluate the usefulness of ad lib feeding for HPS. The authors retrospectively reviewed the records of 116 patients who underwent pyloromyotomy for HPS from 1995 to 2004. Three cases were excluded because of the duodenal perforation during pyloromyotomy. Three feeding-methods were defined as: Conventional feeding (>10 hours nothing by mouth and incremental feeding every 2 hours, C), Early feeding(for 4 to 8 hours nothing by mouth and incremental feeding every 2 hours, E), and Ad lib feeding (for 4 hours nothing by mouth and ad lib feeding, A). Time to normal feeing in C, E and A were 51±24, 34±12 and 24±6 hours, respectively. Hospital-stay in C, E and A were 72±17, 55±13 and 43±12 hours, respectively. There were statistically significant differences according to the method of feeding. Frequency of postoperative emesis in C, E and A were 38%, 47% and 53%, but was not significant statistically. Ad lib feeding decreased time to normal feeding and hospital stay, and did not increase postoperative emesis. We conclude that ad lib feeding is recommended for patient with pyloromyotomy in HPS.