Objective- To determine etiology of Neonatal Hyperbilirubinemia. To assess clinical features of Neonatal Hyperbilirubinemia and Hyper-bilirubinemic Encephalopathy (Kernicterus). To assess risk factors of Neonatal Hyperbilirubinemia. To correlate clinical severity of Hyperbilirubinemia with Transcutaneous Bilirubinometer (TcB) and Total Serum Bilirubin (TSB). Methods: - Hospital based cross-sectional observational study. The study was conducted in the NICU department of Pediatrics at Muzaffarnagar Medical College & Hospital, Muzaffarnagar, U.P. on indoor patients by following inclusion and exclusion criteria, conducting history taking, general physical examination, and relevant clinical examinations, according to predetermined questionnaire. Results: Firstly, concerning birth weight distribution, among the 96 neonates observed, a substantial proportion fell into the lower weight categories, with 47.9 % weighing less than 2500 grams, 29.2% falling within the 2500 to 2999 grams range, and the less, comprising 22.9 %, having a birth weight equal to or exceeding 3000 grams. This variation in birth weight underscores the diversity within the neonatal population. Secondly, the analysis of blood group incompatibility among neonates showed that 18.8% exhibited ABO incompatibility, 12.5% showed Rh incompatibility, while the majority (68.7%) displayed no blood group incompatibility. Thirdly, regarding neonatal jaundice onset time, the majority of cases occurred within the first week post-birth, with 10.4% within 24 hours, 37.5% on days 2-3, and 41.7% on days 4-7. This distribution highlights the critical need for monitoring neonates during this period to detect and manage jaundice promptly. Fourthly, the data on reticulocyte counts (%) in neonates revealed that 41.7% had counts of less than 2%, 37.5% fell within the 2-5% range, and 20.8% had counts exceeding 5%. Conclusion: These findings suggest varying degrees of erythropoietic activity during the neonatal period, which could have implications for overall health and development. The analysis of serum bilirubin levels and clinical severity indicated that 31.3% of neonates exhibited mild clinical severity, 46.9% showed moderate severity, and 21.8% presented severe severity.