Laparoscopic pyloromyotomy is associated with an increased risk of incomplete myotomy compared with open myotomy. We hypothesized that utilizing ultrasound measured length to direct laparoscopic pyloromyotomy would reduce the risk of incomplete pyloromyotomy without a concomitant increase in the risk of mucosal perforation.Infants (n=43) with hypertrophic pyloric stenosis diagnosed by ultrasound and subsequent laparoscopic pyloromyotomy over a 2-year period (December 2006 through December 2008) were studied. Pyloromyotomy length was guided by preoperative ultrasound measurements. Pyloromyotomy was considered complete if the measured length was ≥ the ultrasound measurement. Infants were followed prospectively for time to full feeding, time to discharge, and complications.The cohort included 38 male and 5 female infants (age, 37±13 days; range, 17 to 72 days) who underwent ultrasound (length 1.9±0.2cm; thickness 4.4±0.9mm) and laparoscopic pyloromyotomy. Infants achieved full feeding 28±16 hours postoperatively and were discharged 34±18 hours postoperatively. No infant required reoperation for incomplete myotomy. One infant sustained mucosal perforation (2%). No patient suffered other complications.Preoperative ultrasound measurement of pyloric length to determine the length of laparoscopic pyloromyotomy, rather than visual cues alone, appears to minimize the risk of incomplete pyloromyotomy.