To assess the postoperative restoration of a normal uterine cavity, uterine cavity measurements were obtained in patients with arcuate or septate uteri in the periods before and after resection.Twenty-eight women diagnosed with arcuate or septate uteri were evaluated with 3-dimensional ultrasound before and after undergoing surgical resection by hysteroscopic resection, in a university center. In addition to the conventional parameters, measurements of the subseptum's length and width, and cavity width, were obtained on a frozen coronal view of the uterus. Postoperatively, uterine cavity width was measured.Twelve patients were diagnosed with arcuate uterus and 16 with septate uterus and subsequently underwent surgical correction. Of them, 50% had a retroverted uterus and 61% had a diagnosis of polycystic ovary syndrome (7/28, or 25%, had both). Uterine length, width, and height, before and after resection, were similar between arcuate and septate, as were the subsepti base widths, despite the different lengths. However, cavity width was significantly decreased after resection only in the septate uterus group: 3.6 cm, 95% confidence interval, 3.3–3.9, preoperatively vs 2.8 cm, 95% confidence interval, 2.5–3.1, postoperatively, respectively; P < .001. The postoperative difference in cavity width was directly correlated with the length of the subseptation (r –0.59, P = .05).Postoperative measurements of the uterine cavity revealed a remarkable uterine remodeling capacity: we speculate this could represent the most important single change to explain improved pregnancy outcomes after surgical correction of subseptations.