Five patients with hypertrophic pyloric stenosis are described, in whom protracted jaundice could not be attributed to any other disease. Their course was characterized by indirect hyperbilirubinemia, similar to that in three previously reported cases. It seems reasonable that, in those patients with early onset of jaundice, factors such as physiologic hyperbilirubinemia may account for the early phase, but prolonged or second-phase hyperbilirubinemia may be caused by under-perfusion of the liver as a result of increased intra-abdominal pressure due to the gastric dilatation of pyloric stenosis. Pyloric stenosis should be considered in infants with unexplained protracted or cyclic indirect hyperbilirubinemia.