The T stage is an important criterion for determining prognosis in esophageal carcinoma. Endosonography, although established as a highly accurate method in preoperative determination of the T stage, may be less reliable in non-traversable tumor stenoses. In a comparative prospective study, 41 patients with carcinoma of the esophagus were investigated to determine the role of tumor stenosis on the accuracy of endosonography in preoperative T staging. The results were correlated with the histology of the resected specimen. The overall accuracy in T staging with endosonography was 76%, compared with 49% in computed tomography. T staging results of endosonography were good in easily and non-traversable stenoses (92%, 87% respectively), but lower accuracy was obtained in stenoses which could be traversed only with difficulty (46%). Computed tomography was inferior to endosonography in all three groups of patients. The high accuracy of endosonography in non-traversable stenoses might be due to the fact that all tumors were in an advanced stage (T3 or T4). When passage of the echoendoscope proves difficult, the low focal distance between the ultrasonic transducer and tumor may hamper clear visualisation of the wall layers and tumor penetration depth. These limitations of endosonography should stimulate further efforts in improving ultrasonic resolution in these cases.