Aim: Patent ductus arteriosus (PDA) is a frequent health problem in premature infants. Pharmacologic closure is recommended only for hemodynamically significant PDA (hsPDA) that is defined according to the clinical and echocardiographic criteria. The aim of this study was to explore the value of commonly used criteria in defining hsPDA and predicting the required number of courses of ibuprofen treatment to close PDA in premature infants. Methods: Sixty premature infants with a gestational age of ≤33 weeks were evaluated prospectively. Clinical and echocardiographic criteria O2 requirement, ductus diameter (DD) and left atrial-to-aortic root diameter ratio (LA:Ao) were used to define hsPDA. Clinical improvement after pharmacologic closure of PDA and association between the criteria and required number of ibuprofen courses were investigated. Results: O2 requirement decreased by PDA closure but was not different between patients with hsPDA and the others with PDA. Also, O2 requirement was not found to be associated with required number of ibuprofen courses. DD and LA:Ao were greater in patients with hsPDA. DD was found to be associated with required number of courses of ibuprofen treatment. Conclusion: Although there was an improvement in O2 requirement with PDA closure, echocardiographic criteria were found to be more valuable in defining hsPDA. DD should also be used to estimate the duration of treatment.