A recent alternative feeding regimen at the progressive feeding (PF) after a pyloromyotomy for hypertrophic pyloric stenosis (HPS) is the so-called ad libitum feeding (AL). The aim of this study was to determine if this new feeding regimen has modified the follow-up of postoperative course in HPS. METHODS From January 1998 to December 2003, 97 consecutive neonates have been operated on for HPS in our hospital. This retrospective study was based on the comparison between two groups of patients with different postoperative feeding regimens: group one of 30 neonates with PF regimen and group two of 60 neonates with AL regimen. Seven remaining neonates had had a mucosal perforation and were not included in this comparative study but in a separate group (MP). The clinical, ultrasonographic, operative and postoperative data were compared. RESULTS There was no difference between the PF and AL groups for sex ratio M/F=4/1, preoperative weight loss ratio, ultrasonographic data and intra-operative difficulties rate. A small difference was found - which was not significative - between the PF and the AL groups for median age at diagnosis (44,6 v 36,7 days, respectively). A statistically significative difference between the PF and the AL groups was observed for time to establish feeding (69 vs 35.6 hours, respectively) (P<0,001), postoperative stay (4.16 vs 2.98 days, respectively) (P<0,001) and total hospital charges. We didn't found any difference in the incidence and severity of postoperative emesis whether slow (PF) or rapid (AL) feeding regimens were used. Furthermore, intra-operative mucosal tear didn't influence postoperative course and the duration of hospital stay. CONCLUSIONS We recommend AL regimen for routine feeding in simple cases after pyloromyotomy for HPS. It has a positive impact on length of hospital stay, and decreases hospital charges. Most neonates with MP can be managed with a rapid feeding regimen.