OBJECTIVE: Use axial magnetic resonance imaging to test the null hypothesis that no difference exists in apparent vaginal thickness between women with and those without prolapse. METHODS: Magnetic resonance imaging studies of 24 patients with prolapse at least 2 cm beyond the introitus were selected from an ongoing study comparing women with prolapse with normal control subjects. The magnetic resonance scans of 24 women with prolapse (cases) and 24 women without prolapse (controls) were selected from those of women of similar age, race, and parity. The magnetic resonance files were imported into an experimental modeling program, and 3-dimensional models of each vagina were created. The minimum transverse plane cross-sectional area, mid-sagittal plane diameter, and transverse plane perimeter of each vaginal model were calculated. RESULTS: Neither the mean age (cases 58.6 years +/- standard deviation [SD] 14.4 versus controls 59.4 years +/- SD 13.2) nor the mean body mass index (cases 24.1 kg/m(2)+/- SD 3.3, controls 25.7 kg/m(2)+/- SD 3.7) differed significantly between groups. Minimum mid-sagittal vaginal diameters did not differ between groups. Patients with prolapse had larger minimum vaginal cross-sectional areas than controls (5.71 cm(2)+/- standard error of the mean [SEM] 0.25 versus 4.76 cm(2)+/- SEM 0.20, respectively; P = .005). The perimeter of the vagina was also larger in the prolapse group (11.10 cm +/- SEM 0.24) compared with controls (9.96 cm +/- SEM 0.22) P = .001. Subgroup analysis of patients with endogenous or exogenous estrogen showed prolapse patients had larger vaginal cross-sectional area (P = .030); in patients without estrogen group differences were not significant (P = .099). CONCLUSION: Vaginal thickness is similar in women with and those without pelvic organ prolapse. The vaginal perimeter and cross-sectional areas are 11% and 20% larger in prolapse patients, respectively. Estrogen status did not affect differences found between groups.