Multiple peripheral pulmonary carcinoid tumors or their smaller counterparts (tumorlets of carcinoid type) are the most unusual form of carcinoids as a cause of ectopic corticotropin syndrome. Only three case reports were found in the literature. We describe a 35 year-old female patient with ectopic corticotropin secretion due to multiple peripheral pulmonary carcinoid tumors and tumorlets. A high-dose dexamethasone suppression test result led to the diagnosis of Cushing's disease in our case. But no tumor was identified on sella imaging and bilateral inferior petrosal sinus sampling was non-diagnostic. Computed tomography of the lungs revealed multiple acinar-nodular parenchymal infiltrations confined to the left lung. Corticotropin-dependent hypercortisolism persisted after bilateral adrenalectomy. A second operation was necessary to remove the hyperplastic adrenal remnants. Meanwhile, computed tomography findings of the thorax were unchanged. We decided to explore these nodules by open lung biopsy. During the procedure multiple nodules ranging 12 to 3 mm in diameter scattered throughout the left lung were observed and left pneumonectomy was performed. Histopathological diagnosis was multiple peripheral carcinoid tumors and tumorlets of carcinoid type showing positive immunostaining with corticotropin. This observation emphasizes a rare form of carcinoids as a cause of ectopic corticotropin secretion and its unusual response to high dose dexamethasone suppression test.