Colorectal carcinoma: preoperative TNM classification with endosonography. Transcolorectal endosonography (TES) with use of both a nonoptic instrument and an echocolonoscope was performed in 91 patients with colorectal carcinomas (61 rectal and 30 colonic). Correlation of results at TES with results of histologic analysis of resected specimens according to the 1987 TNM classification demonstrated that TES allowed accurate staging of all tumors except T2 carcinomas, which were often accompanied by peritumoral inflammation or abscesses. Overall, the accuracy of staging rectal and colonic carcinomas with TES was 81% and 93%, respectively; overstaging occurred in 13% and understaging in 2%. For regional lymph nodes, the accuracy of staging with TES was 70%, the sensitivity was 94%, and the specificity was 55%. Correlations between findings at TES and the Dukes classification were as follows: for rectal carcinoma, 48% for class A, 50% for class B, and 96% for class C; for colonic carcinoma, 67% for class A, 46% for class B, and 91% for class C. Overall accuracy was 67%. With the addition of abdominal computed tomographic or ultrasonographic examinations to evaluate distant metastases, TES should become an important imaging technique for clinical TNM staging of colorectal carcinomas. 