Introduction: Cyclic Cushing's syndrome is a not widely known pathology with low incidence; however, an increase in the number of cases has been observed in recent years. The intermittent clinical symptoms and discordant laboratory results make it a complicated diagnosis; therefore, close follow-up is crucial. We describe a case of ectopic cyclic Cushing's syndrome in a woman in her seventies who presented weight gain, proximal myopathy, moderate hypokalemia and uncontrolled hypertension; in the first evaluation hypercortisolism was found, however, 2 months later cortisol presented normal levels. Subsequently, a close follow-up was carried out and the study protocol was continued once the presence of 3 peaks and 2 valleys was demonstrated, obtaining compatible values for ectopic ACTH-dependent cyclic Cushing's syndrome. In thoracoabdominal MRI a spiculated lesion was found in the left basal lung field surrounding 25% of the aorta. Due to the location of the lesion, the patient refused surgical treatment, being currently under adequate control with the use of ketoconazole and octreotide injections. Conclusions: The possibility of cyclic Cushing's syndrome diagnosis should be kept in mind in those patients with symptoms suggestive of Cushing's syndrome that remit sporadically and whose laboratory studies show intermittent results of hypercortisolism and normocortisolism, since early identification allows opportune treatment and therefore better prognosis.