During the last nine years 123 patients with intrathoracic localization of sarcoidosis have been observed. There were six deaths from sarcoidosis. Thirty-nine patients showed varying degrees of pulmonary fibrosis, and eighteen patients among the survivors were left with significant respiratory difficulty. Intrathoracic lesions could be assigned to one of three broad chronologic stages according to the roentgen pattern present on the initial chest film: early, transitional and late. In the early stage, for those patients whose film showed enlarged mediastinal nodes without pulmonary lesions the outlook was best. It was not so favorable for patients whose films showed miliary nodulation of the lung fields and still less favorable when the film first showed a patchy bronchopneumonic pattern. Patients in the transitional and late fibrotic stages often showed disabling symptoms, and five of the six deaths caused by sarcoidosis were in patients with pulmonary lesions in these stages. Scalenus fat pad biopsies and the Nickerson-Kveim intracutaneous reaction are valuable diagnostic aids when involved tissue is not easily accessible for biopsy verification. Cortisone and corticotrophin generally act favorably upon intrathoracic sarcoidosis although the benefits usually prove temporary. In severe pulmonary insufficiency occasionally seen in the early stage and more often in the late fibrotic stage of pulmonary involvement, hormones may be the only means to tide a patient over the crucial period. In early stage lesions consisting of mediastinal lymphadenopathy, treatment is unnecessary because spontaneous regression is the rule. It is still debatable whether patients with asymptomatic miliary nodulation or bronchopneumonic patches in the lung fields should receive hormonal therapy in an attempt to forestall widespread pulmonary fibrosis. In chronic pulmonary sarcoidosis the effects of the hormones are variable. Sometimes symptomatic relief is dramatic and sustained. More often the relief is partial and relapse occurs promptly after the hormones are withdrawn. Pulmonary fibrosis may proceed even while the patient continues to receive the drugs. Indications for the treatment of extrathoracic lesions of sarcoidosis are listed.