Pulmonary malignant angioendotheliomatosis. Presentation with fever and syndrome of inappropriate antidiuretic hormone. A 64-year-old man presented with protracted fever, hyponatremia, and mononeuritis multiplex. Inappropriate antidiuretic hormone secretion was established. The absence of pulmonary infiltrates precluded any lung biopsy. Autopsy revealed malignant angioendotheliomatosis involving multiple organs including the alveolar septa and pulmonary vasculature. An early diagnosis of MAE in the setting of fever and SIADH may be possible via transbronchial biopsy. 