Objectives: The aim of this study was to investigate the features of newborns on the occurrence of intensified and prolonged hyperbilirubinemia in term neonates. Patients and methods: The retrospective research study included 100 term neonates, out of which 42 diagnosed with neonatal hyperbilirubinemia were hospitalized in the Department of Gastroenterology of the “Sestre Milosrdnice” University Hospital in Zagreb and 58 in the Department of Gastroenterology of the University Hospital in Split, in the period between the 1st January 2017 and 10th May 2019. Results: This study included 100 neonates and younger infants with diagnosed intensified (68%) and prolonged hyperbilirubinemia (32%) in the age of 2 to 45 days. In both groups the age of the mother was in the average 30 years. All the children were born in the 39th gestation week and 63% of children were born vaginal delivery. Newborns in the group of intensified hyperbilirubinemia were more often born during the warmer months, March – September, and newborns with prolonged hyperbilirubinemia in the colder part of the year. Most children were treated with intravenous fluid supplements, 89% of them, and 56% children were also treated with phototherapy. The influence of urinary infection on newborn hyperbilirubinemia is not proven. Laboratory findings of erythrocytes, hemoglobin and hemtocrit were within the refining values, and a small number of children had insignificantly elevated liver enzymes. The highest value of bilirubin was measured in the group of intensified hyperbilirubinemia and it was 472 µmol/l. The body mass of the newborns and infants with intensified hyperbilirubinemia was significantly lower on admission compared to the birth weight, whereas in the group of prolonged hyperbilirubinemia children had higher body mass at the time of hospitalization than the birth weight. 42 out of 100 newborns and infants had DNA-UGT analysis at UGT1A1*28 genotype done. The frequency of the polymorphism carrier for Gilbert syndrome in the examined population was higher than the frequency in the control group. Conclusion: Newborn hyperbilirubinemia is a significant clinical entity to which many hereditary, environmental and other factors can be affected. Of all the examined features of newborn hyperbilirubinemia, the strongest correlation was found in the difference in body weight at admission and birth weight, which is negative in the group of intensified hyperbilirubinemia and positive in newborns with prolonged hyperbilirubinemia. GS polymorphism is an important factor influencing the appearance and duration of newborn hyperbilirubinemia. All tested features should be taken into account when assessing the severity of newborn hyperbilirubinemia when discharged from the maternity clinic, in order not to miss a clinically significant hyperbilirubinemia that requires further processing and monitoring.