Ono S, et al. - Medical records of persons with infantile hypertrophic pyloric stenosis (IHPS) who were admitted to Kimitsu Chuo Hospital between 2002 and 2016 and were initially administered atropine sulfate were retrospectively analyzed in order to examine the risk factors for unsuccessful results after IV atropine (IA) for IHPS. Of the 48 individuals with IHPS, 33 were fortunately treated with IA and 15 required surgical intervention. For unsuccessful IA therapy in IHPS, age at diagnosis < 30 days was concluded as a risk factor. Thus, when IA therapy is practiced for neonates with IHPS, this may be taken into consideration.