We would like to respond to the letter from Professor Viroj Wiwanitkit to about our study on hyperbilirubinemia and pelvicaliceal dilatation that was published in the last issue of 2011 of Iran J Pediatr [1]. We have a limitation due to our study sample was small and we did not have follow-up data of the included babies. But we have no patient that has confounding factor (such as genetic disorders that can cause hyperbilirubinemia and/or biliary atresia) in our study population. The reasons for hyperbilirubinemia and urinary tract infection are still not fully understood, however the prevalence of urinary tract infection is increased in hyperbilirubinemic neonates than in healthy children. The potential pathogenetic mechanisms may be some hepatotoxins from the infected gram-negative bacilli, and or especially E coli, which might increase the fragility of red blood cells and the production of hemolysin [2]. We think too, as you indicate, it is not a direct one-step relationship.