Endosonography (ES) was used for the preoperative TNM (1987) staging of tumors in 43 patients with pancreatic cancer and 24 patients with ampullary carcinomas. These results were correlated with the histologic findings of resected specimens. Early-stage tumors could be distinguished from advanced stages of cancer with ES. Detailed images of ductular and parenchymal abnormalities allowed distinction between pancreatic and ampullary carcinomas based on anatomic location. The overall accuracy of ES in the assessment of tumor classification in pancreatic and ampullary carcinoma was 92% and 88%, respectively. In diagnosing regional lymph nodes in pancreatic and ampullary tumors the accuracy of ES was 74% and 54%, respectively. For diagnosing metastatic lymph nodes in pancreatic and ampullary carcinoma the accuracy of ES was 91% and 80%, respectively. The prevalence of lymph node metastases in T1 pancreatic cancers and T1 ampullary carcinomas was 40% and 0%, respectively. Discrimination between inflammation and metastases was difficult with ES. ES was not accurate in assessing distant metastases because of the limited penetration depth of ultrasound.