Deep infiltrating endometriosis (DIE) is characterized by the presence of endometrial tissue outside the uterine cavity that infiltrates at least 5-mm deep below the peritoneal layer. Imagining examinations are the first-choice methods to detect DIE. The aim of this study is to assess whether rectal water contrast transvaginal sonography (RWC-TVS) can be a useful tool for the estimation of the size of deep bowel endometriotic nodules. This retrospective study includes 31 patients subjected to RWC-TVS who underwent surgery due to deep bowel endometriosis between January 2021 and December 2022. Nodule dimensions measured via ultrasound were compared to those of histopathological samples taken after surgery. In total, 52% of patients had endometriosis limited only to the intestines, 19% had endometriotic nodules located at uterosacral ligaments and posterior vaginal fornix, 6% at the anterior compartment, and 13% at a different location. Additionally, 6% of patients had nodules at more than two locations. In all but one case, the intestinal nodules could be seen on RWC-TVS images. The largest nodule dimension measured via RWC-TVS and the size of the equivalent histopathological sample correlated (R = 0.406,p= 0.03). Thus, RWC-TVS allows for the detection of DIE and moderate estimation of the nodule sizes and should be practiced during a diagnostic process.