The most common cause of adrenocorticotropic hormone (ACTH)-dependent Cushing’s syndrome is a benign ACTH-producing pituitary tumour or, less frequently, ectopic ACTH production from non-pituitary tumours. Ectopic ACTH syndrome occurs more commonly in men and usually presents after 40 years. It is most commonly associated with small cell lung cancer. Although this syndrome is associated with severe hypercortisolemia, some findings of Cushing’s syndrome, such as central obesity, may not be observed due to underlying malignant diseases. In these cases, rapid metabolic disruption, anorexia, myopathy, glucose intolerance, hypokalemic alkalosis, and hyperpigmentation accompany the patients’ clinical condition. In the current case report, we aimed to emphasize that ectopic ACTH syndrome should be kept in mind in the differential diagnosis, especially in the presence of hypokalemia accompanying hypertension and proximal muscle weakness, if the patient also has progressive weight loss.