Deep infiltrating endometriosis (DIE) of the rectum and rectosigmoid colon represents one of the most severe forms of endometriosis and often requires surgical management when symptomatic and unresponsive to medical therapy. Accurate preoperative assessment of lesion size, extent, and depth of bowel infiltration is essential to guide surgical planning and minimize complications. Transvaginal ultrasound (TVUS) is the first-line imaging technique for the diagnosis of pelvic endometriosis and has high diagnostic accuracy for detecting rectosigmoid lesions. However, its ability to precisely assess infiltration depth and guide the choice of surgical technique may be limited by anatomical distortion and technical factors. Intraoperative ultrasound (IO-US) is a real-time imaging modality that can be performed during laparoscopic surgery after adhesiolysis, allowing direct evaluation of bowel lesions. It may improve the assessment of lesion characteristics and support intraoperative decision-making, potentially reducing unnecessary bowel resections. This prospective single-center comparative study aims to evaluate the agreement between preoperative TVUS and intraoperative ultrasound in measuring rectal and rectosigmoid DIE nodules. Secondary objectives include assessing measurement differences, identifying factors associated with discordance, and evaluating the reproducibility of ultrasound measurements. The findings of this study may improve preoperative counseling, optimize surgical planning, and support the integration of intraoperative ultrasound into the management of bowel endometriosis.