Purpose: Pancreatic ductal adenocarcinoma (PDAC) is one of the worst cancers, and development of early detection methods and effective therapies for PDAC is needed. The usefulness of ultrasonography for early detection of small-sized PDAC has been suggested, although only limited reports have described in detail the ultrasonographic findings for small-sized tumors using large cohorts. Here we investigated ultrasonographic findings in 46 resected cases of PDAC in which the tumor diameter was 20 mm or less. Subjects and Methods: A total of 46 lesions from 46 patients with PDACs histopathologically determined to be 20 mm or less in diameter were investigated. Specific ultrasonographic findings included tumor size, shape, boundaries, contours, and internal signal intensity, as well as the presence/absence of spinous structures, dilatation of the pancreatic tail-side main pancreatic duct, or cystic components. Contrast-enhanced ultrasonography using Levovist was performed on 17 lesions. Results: Of the 46 lesions, 42 could be visualized as tumors in B mode. The remaining four lesions showed only dilatation and disruption of the main pancreatic duct, although three of them were detected as tumors on contrast-enhanced ultrasonography. The average size of these 45 detectable 45tumors was 15.7 ± 3.8 mm (range 8 - 22 mm). Of the 42 lesions visualized in B mode, 40 (95.2%) were irregularly shaped, 28 (66.7%) were well circumscribed, and all demonstrated irregular contours and low signal intensity. Spinous structures, main pancreatic duct dilatation, and cystic components were observed in 13 (31.0%), 32 (69.6%), and eight lesions (17.4%), respectively. Various levels of contrast effect were observed for the 17 lesions on contrast-enhanced sonography. Conclusions: These results indicate that ultrasonographic findings obtained from small-sized PDACs are almost the same as those usually observed in cases of PDAC in advanced stages. It is suggested that even small-sized PDACs can be diagnosed through detailed ultrasonographic observation.