Various echocardiographic parameters are determined in the assessment and evaluation of a patent ductus arteriosus. In isolation, many of these parameters have a low sensitivity and specificity for ductal hemodynamic significance compared with ductal size. This study aimed to correlate various echocardiographic parameters with ductal size (transductal diameter) in infants with a symptomatic patent ductus arteriosus and to ascertain the accuracy of various parameters in predicting a duct 3 mm in size or larger. In this retrospective study, preterm infants younger than 32 weeks gestation who were evaluated for the presence of a patent ductus arteriosus during the period June 2010-2012 were assessed. The following echocardiographic parameters were measured: transductal diameter (TDD), ductal velocity, end-diastolic left pulmonary artery flow, ductal diameter-to-left pulmonary artery ratio (TDD:LPA), left atrial-to-aortic root ratio (LA:Ao), left ventricular output-to-superior vena cava flow ratio (LVO:SVC), transmitral E:A ratio, and isovolumic relaxation time (IVRT). The study enrolled 52 infants with a mean gestation age of 26 ± 2 weeks and a mean birth weight of 837 ± 240 g. The mean transductal diameter was 2.8 ± 0.5 mm. Transductal diameter correlated significantly with ductal velocity, end-diastolic LPA flow, TDD:LPA ratio, LA:Ao ratio, and LVO:SVC ratio but not with transmitral indices. The LVO:SVC ratio had the highest specificity (0.83) and sensitivity (0.95) for detecting a duct 3 mm in size or larger, the area under the curve being 0.95 (95 % confidence interval [CI], 0.85-0.99). Significant correlations between ductal size and surrogate markers of pulmonary overcirculation were noted.