Immunosuppression with subsequent opportunistic infections is a well-recognized complication of severe hypercortisolism. We report a case of fatal pneumocystis jirovecii pneumonia (formerly pneumocystis carinii pneumonia) in a case of ectopic Cushing's syndrome caused by a neuroendocrine carcinoma of the kidney. The 36-year old male patient had consulted a physician because of weight gain. Further endocrine diagnostic work-up revealed ACTH-dependent hypercortisolism of non-pituitary origin. Because of rapid clinical deterioration therapy with metyrapone was initiated. A neuroendocrine carcinoma of the right kidney with regional lymph node infiltration was identified and was suspected to be the source of the ACTH excess. Before any causal therapy could be initiated, the patient developed severe pneumocystis jirovecii pneumonia and died shortly thereafter from multiorgan failure one month after he first consulted a physician. Pneumocystosis has been reported in only a few cases of Cushing's syndrome. There seems to be a relationship between the degree of hypercortisolism and the susceptibility to opportunistic infections. Since ACTH concentrations may be excessively high in ectopic Cushing's syndrome and pneumocystosis may deteriorate as a consequence of decreasing circulating cortisol levels under adrenolytic therapy, prophylaxis against pneumocystis jirovecii infection should be considered.