We present a case of primary pancreatic small cell carcinoma with an unusual sonographic feature. A 75-year-old woman presented with poor appetite and weight loss. Abdominal sonographic examination revealed a diffusely enlarged pancreas with relative increased echogenicity and smooth contour. CT also confirmed the diffuse infiltrative pattern of the tumor. The diagnosis was confirmed via sonographically guided biopsy. The tumor was composed of small cells with hyperchromatic nuclei and scanty cytoplasm infiltrating the pancreatic tissue, consistent with small cell carcinoma of the pancreas. Primary pancreatic small cell carcinoma rarely presents as the diffuse infiltrating type. These unusual sonographic features must be differentiated from other pancreatic tumors presenting as diffuse pancreatic enlargement. VVC 2006 Wiley Periodicals, Inc. J Clin Ultrasound 35:82–84, 2007; Published online in Wiley InterScience (www.interscience.wiley.com).