PURPOSE:The accuracy of diagnosis of metastatic lymph nodes for rectal carcinoma has not improved. A low echoic lesion more than 5 mm in size detected by endorectal ultrasonography is preoperatively assessed as a metastatic lymph node. What does a low echoic lesion more than 5 mm in size correspond to histologically?METHODS:Forty‐seven patients with lower rectal carcinoma (Term I, 1986‐1990) and 48 patients with lower rectal carcinoma (Term II, 1991‐1995) undergoing endorectal ultrasonography were reviewed. Surgically resected rectal specimens from 40 patients with rectal carcinoma underwent ultrasonography. Low echoic lesions more than 5 mm in size were taken from resected specimens and were stained with hematoxylin, followed by histologic examination.RESULTS:The accuracy of diagnosis of metastatic lymph nodes of Term II was not higher than that of Term I. Twenty‐five low echoic lesions were detected by ultrasonography using 40 resected specimens. Seventeen of these 25 lesions (68 percent) were histologically confirmed to be metastatic lymph nodes. One of 25 (4 percent) was found to be lymphadenitis with no metastasis. Among the 25 lesions, 5 (20 percent) were histologically confirmed to be tumor deposits, 2 (8 percent) fatty tissue, and 22 (88 percent) carcinoma.CONCLUSIONS:Low echoic lesions were histologically confirmed to be tumor deposits (20 percent) and metastatic lymph nodes (68 percent). Although these data show deficiencies and limitations of the accuracy of endorectal ultrasonography, they compare favorably with other series, and no other current technology can show similar accuracy.