OBJECTIVE: To compare the uterine transverse diameter (UTD) in women with normal uteri and women with uterine canalization defects as well as to assess its performance for ruling out such defects. STUDY DESIGN: Retrospective analysis of prospectively collected data in a series of selected women with primary or secondary infertility. Measurement of UTD and 3D volume acquisition subsequent off-line analysis was performed in order to identify possible canalization defects. UTD of the normal uterus, measured by 2D ultrasound, was compared to that of arcuate, subseptate, and septate uteri. ROC curve was plotted to determine the best UTD cutoff for differentiating normal from abnormal uteri. RESULTS: A total of 421 women were ultimately evaluated. UTD was significantly larger in women with (53.3 mm, SD 6.3, p <0.05), subseptate (55.0 mm, SD 6.7, p <0.05), and septate (56.0 mm, SD 4.8, <0.05) uterus as compared with the normal uterus (45.9 mm, SD 7.1). ROC curve showed that the best UTD cutoff for ruling out the presence of a uterine canalization defect was 45 mm (AUC 0.809, 95% CI 0;768-0.849). CONCLUSION: Measurement of UTD may be a simple and practical method for ruling out a uterine canalization defect in infertile women.