The vomiting in pyloric stenosis may or may not be projectile, however non bilious vomiting after feed is the characteristic feature. In about 10-15% of infants vomiting may contain blood. This bleeding is due to reflux esophagitis, a common association with hyperophic pyloric stenosis. Also know: Associated anomalies occur in 6-20% of patients. These includes esophageal atresia, Hirschsprung's disease, anorectal anomalies, and intestinal malformation. Ref: Nelson 17/e, Page 1229.