Accurate preoperative staging is very important to the planning of the appropriate treatment for patients with rectal cancer. The author studied the utility and accuracy of ultrasonography in the detection and staging of rectal cancer. Intrarectal linear scanning with a 5.0 MHz probe by the water enema method was conducted to determine the depth of invasion and degree of lymph node metastasis in 23 cases of lower rectal cancer. Real-time longitudinal tomograms of the rectal wall and adjacent pelvic organs were clearly observed. The normal rectal wall was delineated as a 3- or 5-layer structure. The most hypoechoic layer was the proper muscular layer. The ultrasonograms of cancer and lymph node tissue were hypoechoic and heterogeneous. The depth of invasion was evaluated from the destruction of the layer structure. The overall accuracy rate was 82.6% . Misdiagnoses were mostly overestimatious. The metastatic lymph node was shown as a round shaped lesion. In the diagnosis of lymph node metastasis, 82.6% of the cases were diagnosed correctly, with 100% sensitivity and 71.4% specificity. The ultrasonogram also provided information about the extent of lateral and distal cancer spread. The cases diagnosed as Dukes A by this method may be indicated for function preserving operations. It was concluded that this new imaging method is very useful for precise preoperative staging and choice of operative procedure.