Purpose To evaluate the performance of translabial (TL) US in preoperative detection of sling erosion into pelvic organs with cystourethroscopic and surgical correlation. Materials and Methods The study cohort included women who underwent surgery at a subspecialty center (from 2008 to 2016) for suspected mesh complications in the setting of previous midurethral sling placement for stress urinary incontinence (from 1999 to 2012) with available preoperative TL US imaging. Clinical information, the finding of sling erosion identified intraoperatively and at cystourethroscopy, and blinded dual-reader radiologic analysis of the TL US studies for mesh location (intraluminal, mural, or extramural) relative to pelvic organs (bladder, urethra, vagina, or rectum) were evaluated. The diagnostic performance of TL US was correlated with the reference standard of surgical findings. The consensus of two radiologists was recorded, and interobserver agreement was evaluated with the κ statistic. Results Of the 124 women who were suspected of having sling erosion (mean age, 57.5 years ± 11.1 [standard deviation]), 15 women (12.1%) had sling erosion into the urethra or bladder at surgery. Sensitivity and specificity for erosion at TL US were 53% (95% confidence interval: 45%, 62%) and 100% (95% confidence interval: 97%, 100%), respectively, when erosion was defined as only intraluminal mesh products. Sensitivity and specificity for erosion at TL US were 93% (95% confidence interval: 89%, 98%) and 72% (95% confidence interval: 65%, 80%), respectively, when erosion was defined as visualizing either intraluminal or intramural mesh products. Interobserver agreement (κ value) was 0.95. Cystourethroscopy had 67% sensitivity and 100% specificity for sling erosion. Conclusion Preoperative translabial US can be used to detect sling erosion into the lower urinary tract, with sensitivity up to 93% and specificity up to 100%. © RSNA, 2018 Online supplemental material is available for this article. See also the editorial by Benson and Phillips in this issue.