We present a patient with a poorly differentiated squamous cell carcinoma of the left lower lobe, who developed Cushing's syndrome. Adrenocorticotrophic hormone (ACTH) and cortisol levels in the blood were extremely elevated, but immunostaining for ACTH and corticotrophin releasing factor (CRF) of the primary tumour and metastases was negative. The ectopic Cushing's syndrome was probably caused by CRF-like production.