['The aim of the study was to evaluate the accuracy and reproducibility of fetal crown-rump length (CRL) measurement using three-dimensional ultrasound (3DUS).', 'We included a series of women with singleton pregnancy at 6-13 + 6 weeks. Following CRL measurement by the two-dimensional ultrasound (2DUS), a 3DUS volume was acquired. On the reconstructed midsagittal plane, CRL was measured twice by an operator and once by another. The correlation between CRL measured by 3DUS and 2DUS, as well as the intraobserver and interobserver agreement, was then calculated. Furthermore, the agreement between 2DUS and 3DUS CRL measurements together with intraobserver and interobserver agreement was calculated separately for the groups with a midsagittal acquisition plane (MSAP) and non-midsagittal acquisition plane (NMSAP).', 'Overall, 137 pregnancies were included in the analysis. CRL measurements performed using 3DUS showed excellent correlation with 2DUS [intraclass correlation coefficient (ICC) = 0.992]. In addition, the 3DUS showed a high intraobserver and interobserver agreement (ICC = 0.999 and 0.993, respectively). Finally, when we divided the acquired volumes according to the plane of acquisition, excellent 2DUS-3DUS, as well as intraobserver and interobserver agreement, was maintained for both MSAP and NMSAP.'] Is three-dimensional ultrasound an accurate and reproducible technique for fetal crown-rump length measurement?