Pancreatic endocrine tumors ore uncommon. Although the great majority of these tumors are well differentiated, their malignant potential varies sometimes greatly. Thus, a variety of clinicopothologic features have been developed in the post to assist in distinguishing pancreatic endocrine tumors with benign, indeterminate and aggressive behavior. Recently, a revised classification of pancreatic endocrine tumors has been proposed including, in addition to previous parameters, the number of mitoses and a Ki-67 index. In this review, the potential diagnostic utility of these different criteria is discussed.