OBJECTIVE: Compare urogenital hiatus size in normal women and women with pelvic organ prolapse. METHODS: The sagittal and transverse urogenital hiatus diameters were measured and hiatus area calculated in 300 women whose support was scored using a modified Baden system. RESULTS: In women with normal support and without prior surgery, hiatus area was 5.4 cm2 (+/-1.71 standard deviation [SD], n = 197). In women with uncorrected clinical prolapse (grade 2-3), the area of the hiatus was enlarged (9.6 cm2 +/- 3.97, n = 34, P < .05) and became larger with progressive prolapse (grade 0, 5.4 cm2 +/- 1.71, n = 197; grade 1, 7.3 cm2 +/- 1.91, n = 27; grade 2, 8.3 cm2 +/- 2.45, n = 18; grade 3, 11.0 cm2 +/- 4.90, n = 16). When matched for age and parity, prolapse patients had a larger hiatus than normal women. Women with recurrent prolapse had a larger hiatus than cured women (13.3 cm2 +/- 3.86, n = 8 compared with 8.1 cm2 +/- 2.44, n = 16, P < .05) or women with recurrence after one operation (8.9 cm2 +/- 1.77, n = 18, P < .05). Hiatus size in patients surgically cured (8.3 cm2 +/- 2.44, n = 16) did not return to normal (5.4 cm2 +/- 1.71, n = 197, P < .05). Increasing area of the hiatus was correlated with an increase in anterior-posterior diameter (r2 = 0.9, P < .05), was less attributable to increased transverse diameter (r2 = 0.6, P < .05), and was not related to thickness of the perineal body (r2 = 0.0, P > .05). CONCLUSION: Increasing pelvic organ prolapse is associated with increasing urogenital hiatus size; the hiatus is larger after several failed operations than after successful surgery or single failure.