Between 10 percent and 20 percent of patients with hypercortisolism (Cushing syndrome) have ectopic production of adrenocorticotropin hormone (ACTH) that causes cortisol excess. In approximately 50 percent of these patients, the source of ACTH cannot be found despite very detailed and extensive examination including imaging studies such as computed tomography scanning, magnetic resonance imaging, and octreotide scan using the conventional low dose of indium-111 pentetreotide ([(111)In-DTPA-D-Phe]-pentetreotide). The sensitivity and specificity of these imaging studies depends on anatomic alterations and/or the dose and adequate uptake of radiopharmaceutical. In contrast, positron emission tomography (PET) has the ability to detect pathologic tissue based on physiologic and biochemical processes within the abnormal tissue. This protocol tests whether [18F]-L-3,4-dihydroxyphenylalanine (18F-DOPA) or use of a higher dose of [111In-DTPA-D-Phe]-pentetreotide can be used to localize successfully the source of ectopic ACTH production. In addition the study examines whether administration of the glucocorticoid antagonist mifepristone can improved the sensitivity of the standard dose [111 In-DTPA-D-Phe] pentetreotide. Patients participating in this arm of the study will have a second standard dose scan rather than a higher dose scan. Others will receive a higher dose octreoscan instead.