A 57 year old man presented with a two week history of right sided chest pain. An admission chest x-ray examination revealed a 2 by 1 cm. lytic lesion of the ninth right rib and right sided pleural effusion. The patient underwent a right thoracotomy during which 700 cc. of blood tinged pleural fluid was drained and a 10 cm. segment of the right ninth rib was excised. The rib lesion showed classic features of eosinophilic granuloma of bone. Cytologic examination of the pleural fluid disclosed abundant histiocytes and eosinophils, consistent with eosinophilic granuloma invading the pleural space. This case is unusual because of the age of the patient and the development of a pleural effusion secondary to the rupture of the tumor into the pleural cavity, the latter not previously reported in the literature.