The prognosis of patients with cancers of the colon or rectum is strongly correlated with the stage of disease at the time of diagnosis. This staging is determined by an assessment of the depth of local penetration (T classification) and the presence or absence of nodal or distant metastases (N and M classification, respectively). For tumors of the proximal colon, decisions regarding surgical technique are, in most instances, made independently of stage. Optimal management of rectal neoplasms, however, is critically dependent upon accurate preoperative localization and staging. At present, endoscopic ultrasound represents the only imaging modality that can directly visualize the individual tissue layers of bowel wall. As such, endoscopic ultrasound is uniquely suited to the preoperative evaluation of these tumors. This article describes the techniques involved in performing accurate preoperative endosonographic evaluation of colorectal malignancies and other miscellaneous lesions of the colon and rectum.