Objective To determine the incidence of late pulmonary hypertension (late PH) in congenital diaphragmatic hernia (CDH) and whether prolonged treatment with noninvasive inhaled NO therapy delivered through a nasal cannula (NC) would sustain pulmonary vasodilation during a period of transition from mechanical ventilation to spontaneous breathing. Study design We collected data on all patients with a diagnosis of CDH admitted to the Children's Hospital, Denver, from January 1996 through December 2001. Patients who had suprasystemic pulmonary hypertension when inhaled NO was discontinued before extubation were treated with inhaled NO delivered with the nasal cannula. Results Newborn infants (n = 47) with CDH were treated during this time period. Short-term (<3 months) and long-term (>1 year) survival was 85% and 75%, respectively; 30 newborn infants were treated with inhaled NO (64%). Inhaled NO was successfully discontinued in 16 patients before extubation, and 10 (21%) were treated with inhaled NO through NC after extubation because of pulmonary hypertension and marked hypoxemia when trials off inhaled NO were performed. Nasopharyngeal NO concentrations were 5.4 ± 0.5 ppm and 2.4 ± 0.4 ppm with inhaled NO measured proximally in the delivery device at 10 and 5 ppm, respectively. Conclusions Late PH occurs in a significant subset of newborn infants with CDH. Noninvasive inhaled NO treatment may reduce the duration of mechanical ventilation while safely treating late PH. (J Pediatr 2003;142:397-401)