Twenty-one infants with the diagnosis of persistent pulmonary hypertension had serial assessments of growth and neurologic development through 12 months of corrected age. Seven infants (30%) had one or more adverse physical outcomes during the first year of life. Four infants (19%) had severe neurologic impairment; seven babies had mild to moderate delay, and 11 babies were found to have no abnormality. Adverse outcome was related to significantly to the duration of hyperventilation, such that the infants without and with abnormalities spent 60 +/- 53 hours and 124 +/- 52 hours hyperventilated, respectively (P less than .01). Our results show that the need for prolonged hyperventilation in infants with persistent pulmonary hypertension is associated with poorer neurodevelopmental outcome.