High serum bilirubin is antioxidant and cytoprotective. We evaluated if urine samples of hyperbilirubinemic newborns impede uropathogenic Escherichia coli growth. Bag- urine samples of hyperbilirubinemic newborns (study group) were cultured at presentation and during remission. Urine sample were obtained only once from healthy newborns (control group). Escherichia coli [2 x 104 colony- forming unit (cfu)/mL] was inoculated into the sterile urine samples and colony counts were determined after 24 h. Bilirubin levels at presentation and remission were also recorded. Escherichia coli colony counts of the control versus study groups and of the presentation versus remission samples in the study group were compared. There were 13 study and 17 control cases. Escherichia coli colony counts were not different in the study group at presentation versus remission (5.4 +/- 0.7 vs. 5.5 +/- 0.8 log(10), respectively; p = 0.659). Escherichia coli colony count of the control group (5.2 +/- 0.6 log(10)) was also not different from the study group. In conclusion, the urine of hyperbilirubinemic newborns did not affect the growth rate of uropathogenic E. coli.