Pancreatic neuroendocrine neoplasms (PNENs) are relatively rare with a reported incidence of 1-2/100,000 and generally thought to originate from the precursor of the neuroendocrine cells including the islet and the pancreatic duct cells. About 65% of PNENs are non-functional. While insulinomas and gastrinomas are the most common functional PNENs, ACTH-producing PNENs are extremely rare. We herein present an extremely rare case of a patient with Cushing's syndrome caused by PNEN. A 46-year-old woman with edema in bilateral lower extremities and moon face was admitted with a suspicious pancreatic tumor. Enhanced computed tomography and endoscopic ultrasonography revealed a pancreatic tumor. The final diagnosis of ACTH-producing PNEN with Cushing's syndrome was based on clinical and biochemical test results and endocrinological studies. The symptoms associated Cushing's syndrome improved after pancreaticoduodenectomy for PNEN.