Purpose: This study aimed to identify the risk factors of persistent pulmonary hypertension of the newborn (PPHN) in neonates with respiratory diseases. Methods: We retrospectively analyzed 58 term newborn infants with respiratory diseases who were admitted to the neonatal intensive care unit of the Seoul Eulji Hospital between January 2008 and July 2014 and required airway intubation and mechanical ventilation within 24 hours of admission. The infants were divided into a PPHN group and a non-PPHN group. Their clinical characteristics; diagnoses at admission; initial blood test results; and changes in vital signs, blood gas analysis results, and ventilator parameters that occurred within 48 hours of admission were investigated. Results: There were 16 infants in the PPHN group and 42 infants in the non-PPHN group. The incidence of secondary PPHN was 27.6%. The incidence of PPHN was significantly higher in infants with respiratory distress syndrome (RDS) associated with extrapulmonary air leakage and meconium aspiration syndrome (MAS) with secondary RDS as the cause. Respiratory rate over 80 breaths/min (P=0.032, OR 11.3, 95%, CI 1.23-103.57) and FiO 2 over 0. 8 (P=0.013, OR 16.8,), when measured 6 hours after admission, were found to be statistically significant risk factors. Conclusion:The results suggest that there is an increased risk of PPHN during treatment of respiratory diseases when aggravation of tachypnea and increase in ventilator parameters are observed after 6 hours of admission.