Abstract: BACKGROUND: Patent ductus arteriosus (PDA) diameter is a frequently measured echocardiographic parameter when assessing the PDA. Though, there are recommendations to use 2D echocardiography to measure the PDA diameter, there is paucity of data on how PDA diameter compares when measured using 2D and color echocardiography. The aim of this work was to examine the bias and limits of agreement between measuring PDA diameter using color and 2D echocardiography in newborn infants. METHODS: This retrospective study examined the PDA using the high parasternal ductal view. Using colour compare, three consecutive cardiac cycles were used to measure PDA diameter at the narrowest point where the PDA joined the left pulmonary artery in both 2D and colour echocardiography by a single operator. RESULTS: The bias between PDA diameter using color and 2D echocardiography was examined in 23 infants (mean gestation: 28.7weeks). The mean (SD, 95% LoA) bias between color and 2D were 0.45(0.23, –0.005 to 0.91) mm. CONCLUSION: Color measurements exaggerated PDA diameter measurements when compared to 2D echocardiography.