Summary A man of 41 years old develops simultaneously signs of mediastinal irritation and endocrine disturbances. One year later, a typical Cushing’s syndrome is observed (adiposity, striæ atrophicæ, disturbances of sugar metabolism, testicular atrophy). At autopsy, the hypophysis does not contain any adenoma but displays typical alterations of the basophilic cells. There is a colloid goiter, bilateral hyperplasia of the adrenal’s cortex, arrest of spermatogenesis and centrolubar liver fat degeneration. In the upper region of the mediastinum, at the location of the thymus, is a small-celled carcinoma with pleural metastases. Its structure and vascularisation suggest that it may have endocrine activity. Five similar cases have so far been reported. The origin of the endocrine distrubances and their relations to the malignant growth are discussed.