For rectal cancer, the decisions about neoadjuvant therapy, radical resection, or local excision depend on accurate preoperative staging. Multiple modalities are available to stage rectal cancer, including digital rectal examination, computed tomography, magnetic resonance imaging (MRI), and endorectal ultrasound (ERUS). Digital rectal examination accuracy varies from 58% to 88% for depth of penetration. Computed tomography accuracy varies from 53% to 94% for depth of penetration and from 54% to 70% for lymph node metastases. Magnetic resonance imaging accuracy varies from 66% to 92% for depth of penetration and from 60% to 90% for lymph node metastases. Endorectal ultrasound varies from 62% to 92% for depth of penetration and from 64% to 88% for lymph node metastases. In all radiologic modalities, overstaging and understaging occurs. Endorectal ultrasound has the advantage of being portable and often office-based, requiring only minimal preparation and is well tolerated by the patient.Although MRI with the use of an endorectal coil may have a slightly higher accuracy for detecting lymph nodes, ERUS has been shown to be the most accurate method for the determination of the depth of wall penetration, and is comparable for lymph node metastases. Interpretation varies with operator experience.Three-dimensional (3D) ERUS may further improve staging accuracy. Endorectal ultrasound is an accurate method to preoperatively stage rectal cancers.Although operator-dependent, it can be readily performed at the time of patient evaluation with minimal preparation or patient discomfort. We are prospectively evaluating modifications to the current staging system and the use of 3D ERUS.