Abstract Background: This study compared the rates of decrease in serum bilirubin levels in severely jaundiced healthy term infants given oral or intravenous fluid supplementation during phototherapy. Methods: A randomized controlled study was carried out in the neonatal intensive care unit of Zeynep Kamil Maternity and Children Hospital (Istanbul, Turkey) over a 4-month period. Two hundred fifty healthy term infants with hyperbilirubinemia were randomized to receive either solely breastmilk (n=125) or both breastmilk and intravenous fluid (n=125) during phototherapy. Results: There were no significant differences (p>0.05) in the mean birth weight, mean gestastional age, modes of delivery, mean time of admission age, mean serum osmolality, and hematocrit and reticulocyte count between the two groups. Similarly, there was no significant difference (p>0.05) in the mean indirect serum bilirubin level at the time of admission to the neonatal intensive care unit and at 4, 8, 12, 24, and 48 hours after commencement of phototherapy between the two groups. There was no significant difference (p>0.05) in the mean duration of phototherapy or in the median duration of hospitalization between the two groups. Conclusions: Based on our results, intravenous fluid support has no effect on the rate of decrease in serum bilirubin and decrease in duration of phototherapy in healthy term newborns with no dehydratation. However, using the oral route avoided the need for intravenous cannulae and their attendant complications. Insensible fluid loss is increased during phototherapy, so protection of hydration status with oral feeding is important for newborns.