The aim of this study was to evaluate the efficacy and accuracy of endoscopic ultrasound (EUS)-guided fine-needle aspiration (FNA) in the diagnosis of pancreatic endocrine tumors and to analyze their cytomorphology. Between March 1999 and June 2004, a total of 30 patients with a cytological diagnosis of pancreatic endocrine tumors were found. Their records were retrieved and the cytological materials were analyzed. The mean size of the tumors assessed by EUS was 3.0 cm. Immediate preliminary interpretation was rendered after an average of 1.5 passes. Based on the cellular patterns, cases were divided into three categories: loosely cohesive aggregates, discohesive single cells, and cohesive flat sheets. Most tumor cells had abundant cytoplasm and eccentric nuclei. Chromatin was fine or coarse but was evenly distributed in all cases. Nuclear pleomorphism, multinucleation, intranuclear inclusions, mitotic figures, and necrosis were seen. Immunohistochemical (IHC) studies on cell blocks confirmed the diagnosis in all cases. EUS-guided FNA is efficient and accurate in establishing the diagnosis of pancreatic endocrine tumors. The variety of cellular patterns presents several differential diagnostic issues that should be considered to avoid erroneous interpretation. Diagn. Cytopathol. 2005;32:204–210. © 2005 Wiley-Liss, Inc.