We report a case of severe ectopic ACTH-dependent Cushing's syndrome secondary to a pulmonary NET, highlighting the importance of multidisciplinary management, advanced imaging with positron emission tomography/computed tomography with gallium-68-labelled DOTA-D-Phe-Tyr-octreotide (68Ga-DOTATOC PET-CT) and aggressive biochemical control to enable curative surgery and full clinical recovery.<h4>Learning points</h4>Ectopic ACTH secretion should be suspected in cases of severe, rapidly progressive hypercortisolism with marked hypokalaemia. This evidence concerns the gene POMC and Cushing syndrome.