Abstract: Objective: To conclude the preoperative detection rate of perirectal lymph nodes with transrectal ultrasonography (TRUS) and to analyzed factors affecting the detection rate and the correlation between the size and metastasis of the lymph nodes. Methods: Preoperative TRUS was conducted for 45 patients with rectal carcinoma and the size and number of the lymph nodes detected by ultrasonic inspection were recorded. The postoperative sonography was performed again for the surgical specimens. All the results were compared with pathologic findings. Neither radiotherapy nor chemotherapy was conducted preoperatively in the cases studied. Results: A total of 698 lymph nodes were detected by pathological examinations. In comparison with the pathological findings, the overall preoperative detection rate of the perirectal lymph nodes by the TRUS was 22.5%, among which the detection rate of lymph nodes of less than 5mm in maximum diameter (L) by TRUS was 12.6%, the detection rate of the lymph nodes with the diameter size of larger than or equal to 5 mm and less than 10 mm amounted to 42.4%, and that with the size of larger or equal to 10 mm was 67.9%. The detection rate of TRUS for the perirectal lymph nodes was relatively low as tumor was found at the superior segment of rectum or causing an obvious stenosis of enteric cavity, with 12.1% and 10.3%, respectively. The pathological findings showed that the incidence rate of lymphatic metastasis in the lymph nodes with less than 5 mm was 13.2%, the incidence of metastasis in the lymph nodes with 5 to 10 mm amounted to 30.7% and that in the lymph nodes with larger than or equal to 10 mm was 64.3%. Conclusion: The detection rate of perirectal lymph node with TRUS is low. The following factors may affect the detection rate of lymph nodes with TRUS: size of lymph node, rectal stenosis, tumor location and atypical ultrasonogram. Check failure of the lymph nodes decreases the accuracy of TRUS in the assessment of perirectal lymph node metastasis.