Abstract. Background: Some neonatologists question whether patent ductus arteriosus (PDA) closure in premature infants is necessary because interventions to promote ductal closure have not been shown to improve long term outcomes. To date, no study has investigated how neonatologists and pediatric cardiologists manage PDA in the era of antenatal steroids and surfactant use. Objectives: To determine the degree of practice variation among neonatologists and pediatric cardiologists in the diagnosis and therapeutic interventions for PDA in premature infants. Methods: Surveys were sent by standard postal mail service to neonatologists (n = 1280) and pediatric cardiologists (n = 758) listed in the directories of neonatal-perinatal medicine and pediatric cardiology training programs in the United States. Result: The overall response rate was 46% (946 of 2038). There was agreement between neonatologists and pediatric cardiologists for clinical signs and symptoms used to diagnose hemodynamically signiﬁcant patat ductus arteriosus (hsPDA). In contrast, echocardiographic parameters used to identify hsPDA differed between subspecialists. With regard to intervention, both neonatologists and pediatric cardiologists recommended treating hsPDA. Almost half of neonatologists employed a practice of prophylactic treatment of PDA, although primary reasons for using prophylactic strategies were signiﬁcantly different between subspecialist groups. Conclusion: There is considerable practice variation in diagnostic echocardiographic criteria and treatment of PDA in preterm infants among neonatologists and pediatric cardiologists. Further investigations are needed to determine whether speciﬁc echocardiographic parameters are associated with successful treatment, and the relation to outcomes in this population.