The objective of the present study is to compare the cytologic features of islet cell tumor (ICT) of pancreas obtained by endoscopic ultrasound guided fine needle aspiration (EUS-FNA) and computed tomography guided FNA (CT-FNA). We also describe the cytologic features associated with malignant ICT. Eleven cytology samples from 121 CT- FNA and 30 EUS- FNA of the pancreas were obtained from nine patients with ICT. Diff-Quik, Papanicolaou, and immunohistochemical stains to determine neuroendocrine differentiation and the hormonal status were evaluated. Cytologic features and specimen adequacy were compared between the two techniques. Cytologic features noted in both benign and malignant ICT were also compared. Nine patients (5 men, 4 women) ranging in age from 29 to 84 years (mean age, 53.8 years). Diagnoses consisted of benign (4) and malignant (5) ICT. EUS-FNA was superior to CT-FNA in obtaining adequate cells (2/2 v 7/9) for the diagnosis and increased cellularity to perform additional immunohistochemical stains (2/2 v 4/7). Single, plasmacytoid cells with finely granular chromatin distribution characterized ICT on cytology. Mitoses (3/5) and necrosis (1/5) were noted in malignant ICT but not in benign ICT. EUS-FNA is superior to CT- FNA for obtaining cells for the diagnosis of ICT. Detection of mitoses and or necrosis from patients with ICT should initiate a search for metastasis.