The clinical and biological findings in six infants with congenital hypertrophic pyloric stenosis with associated jaundice are described. Pathogenesis of this association is not known but current hypothesis are based on either a decrease in the activity of hepatic glucuronyl transferase or an increase in the activity of intestinal glucuronidase. Correction of dehydration and alkalosis does not modify the hyperbilirubinemia which only disappears after pyloromiotomy.