Malignancies of the gallbladder, including neuroendocrine tumors, are uncommon, mostly found incidentally after cholecystectomy and are frequently asymptomatic in the early stages, but highly fatal. Limited data is available on adrenocorticotropic hormone (ACTH) producing neuroendocrine tumors specifically originating from the gallbladder. We report the clinical and radiographic findings, which included positron emission tomography and computed tomography, of a patient with a gallbladder mass who presented with Cushing’s syndrome. Subsequently, a diagnosis of ACTH-producing large cell neuroendocrine carcinoma of the gallbladder was made. Despite being rare and having a poor prognosis, hormone-producing neuroendocrine tumors should be part of the differential diagnosis in the approach of patients with Cushing’s syndrome. Malignancies of the gallbladder, including neuroendocrine tumors, are uncommon, mostly found incidentally after cholecystectomy and are frequently asymptomatic in the early stages, but highly fatal. Limited data is available on adrenocorticotropic hormone (ACTH) producing neuroendocrine tumors specifically originating from the gallbladder. We report the clinical and radiographic findings, which included positron emission tomography and computed tomography, of a patient with a gallbladder mass who presented with Cushing’s syndrome. and having a poor prognosis, hormone-producing neuroendocrine tumors should be part of the differential diagnosis in the approach of patients with Cushing’s syndrome.