Sarcoidosis is a systemic granulomatous process of unknown cause. Pathologically, it is characterized by noncaseous granuloma, and in more than 90% of patients, the lung or intrathoracic lymph nodes are affected. A roentgenographic staging system (stages I, II, and III), based on the appearance of the plain chest roentgenogram, conveys important information about prognosis, degree of symptoms, and pulmonary function abnormalities. The diagnosis should be confirmed by histopathologic examination and exclusion of known causes for the noncaseous granulomatous reaction. When indicated, treatment with alternate-day regimens of prednisone is highly effective. Serial chest roentgenography, pulmonary function studies, and the serum angiotensin-converting enzyme level are useful for monitoring the course of the disease.