The aim of the study was to compare the main body of the external anal sphincter (EAS) cross-sectional area (CSA) of women with and without pelvic organ prolapse. Pelvic magnetic resonance imaging (MRI) scans of 40 women were selected for analysis. Of these women, 20 had pelvic organ prolapse and 20 had normal support. Of the women with normal support, 10 had known major levator ani (LA) muscle defects and 10 had normal LA muscles. The same was true for the women with pelvic prolapse: half had major LA defects and half had no LA defects. All patients had previously completed pelvic MRI in the supine position. 3-D models of the EAS were made and CSA of the EAS perpendicular to the fiber direction were measured circumferentially at 30 degrees intervals. Univariable and multivariable analyses were performed. The mean CSA did not significantly differ between women with prolapse and normal support regardless of LA defect status (normal/-LA defect = 1.13 cm(2), prolapse/-LA defect = 0.86 cm(2), p = 0.065; normal/+LA defect = 1.08 cm(2), prolapse/+LA defect = 1.28 cm(2), p = 0.28). Women with prolapse and LA defects had a 49% larger mean muscle CSA compared to prolapse patients without LA defects (p = 0.01). This difference associated with defect status in prolapse patients was not seen in women with normal support. Women with prolapse alone had external anal sphincter CSAs that were comparable to women with normal support. However, women with both prolapse and a major levator ani defect had larger external anal sphincter CSAs compared to prolapse patients without levator ani defects.