We evaluated the usefulness and limitations of endoscopic ultrasonography (EUS) in pancreatic mass lesions. EUS was useful in detecting small pancreatic mass lesions, especially ductal adenocarcinomas smaller than 20 mm and small islet cell tumors smaller than 10 mm. In some of these cases, characteristic echo patterns were specific and useful for differential diagnosis from focal pancreatitis. However, when EUS did not clearly delineate a tumor at the stenotic area of the main pancreatic duct, transpapillary pancreatoscopy and biopsy/cytology were sometimes effective to obtain a definitive diagnosis. EUS fine-needle aspiration should be performed in conjunction with imaging modalities when the differential diagnosis of a pancreatic mass is difficult to make. Although the value of EUS in cancer staging was overestimated, EUS in conjunction with spiral computed tomography or magnetic resonance imaging should be performed for such a purpose. Usefulness and limitations of intraductal ultrasonography (IDUS) also were evaluated. IDUS was useful in detecting carcinoma in situ and small tumors and in assessing parenchymal invasion and the intraductal spread of the tumor. IDUS was also useful in accurately localizing islet cell tumor and in differentiating benign from malignant cases of localized stenosis of the main pancreatic duct. Thus, EUS and IDUS are indispensable modalities in the diagnosis of pancreatic diseases.