Objectives: We wanted to investigate whether hyperbilirubinemia (significant or physiological) has an effect on breastfeeding, milk intake, infant's wakefulness, and if any, which level of bilirubin affects breastfeeding. Materials and Methods: Healthy, term, and breastfed babies with significant hyperbilirubinemia who required phototherapy were included in the study (group 1, n = 71). In the neonatal outpatient clinic, a control group was formed from babies with physiological jaundice (group 2, n = 90). All infants were monitored during breastfeeding and breastfeeding was evaluated with breastfeeding assessment tools (IBFAT and LATCH) and milk intake was assessed by test scale. The same examinations were repeated after phototherapy when normal bilirubin levels were reached. Results: Milk intake, Infant Breastfeeding Assessment Tool (IBFAT) (IBFAT total score [IBFAT(T)], IBFAT first item score [IBFAT(1)], IBFAT sixth item score [IBFAT(6)]), and LATCH scores were significantly lower in group 1 than the control group (p = 0.001). In group 1, the amount of milk intake, IBFAT and LATCH scores after phototherapy increased significantly compared to prephototherapy values (p = 0.001). Looking at the correlation matrix in the whole study group (groups 1 and 2) there were moderate but very significant negative correlations between bilirubin and milk intake (r = 0.32, p = 0.001), IBFAT(T) (r = 0.47, p = 0.001), IBFAT(1) (r = 0.57, p = 0.001), IBFAT(6) (r = 0.65, p = 0.001), and LATCH scores (r = 0.49, p = 0.001). In the receiving operating characteristics analysis, the cutoff bilirubin value was found to be 12 mg/dL. Conclusion: Hyperbilirubinemia may have a negative effect on breastfeeding and milk intake. It appears that bilirubin levels above 12, including in babies with physiological jaundice, adversely affect breastfeeding.