Immunologic and nonimmunologic events lead to significant graft loss after islet transplantation. Unfortunately, current metabolic testing methods are inadequate to detect many of these changes, leading to a critical need for noninvasive monitoring of islet rejection. However, their small size and distribution after transplantation pose specific problems for direct islet imaging. This article reviews the relative merits of several imaging modalities for the noninvasive monitoring of islet transplantation and rejection.