Purpose <p>Rectal prolapse (RP) is a clinically significant condition with vaginal delivery as a major risk factor, especially in elderly females, needs precise evaluation for guiding treatment. Given the limitations of current diagnostic methods in terms of convenience, this study aims to develop an improved measure for RP.</p> Methods <p>A retrospective analysis of 181 female patients undergoing both dynamic three-dimensional transperineal ultrasound (3D-TPUS) and radiographic (X-ray or MRI) defecography (X-ray and MRI) was conducted to investigate the correlation between 3D-TPUS parameters and RP severity.</p> Results <p>Relative to mild RP cases, severe RP patients were older, had heavier neonatal birth weight, and less nulliparous individuals. Significant differences in severe RP cases were demonstrated by 3D-TPUS quantification, greater levator hiatal area enlargement (LHA), increased bladder neck descent (BND), and deeper rectal ampulla position (RAP) compared to mild cases. Significant predictors of severe RP identified by univariable logistic regression included age, vaginal parity, RAP, and LHA. Multivariable logistic regression analysis exhibited that age and LHA during Valsalva were the most influential indicators of severe RP. Receiver operating characteristic (ROC) curve analysis revealed that an LHA ≥ 17.5 cm² is indicative for screening (sensitivity 90%, specificity 16.7%), and an LHA ≥ 32.5 cm² serves as a reference threshold for surgical referral (sensitivity 26.8%, specificity 90%).</p> Conclusions <p>Dynamic 3D-TPUS-measured LHA associated with with RP severity and could serve as a quantifiable marker for pelvic floor dysfunction in RP. This study introduces an adjunctive indicator for the severity of RP, improving diagnostic convenience and patient management.</p> Graphical Abstract <p></p>