Sarcoidosis is a systemic disease of unknown etiology characterized by the presence of noncaseating granulomas in any organ, most commonly the lungs and intrathoracic lymph nodes. A diagnosis of sarcoidosis should be suspected in any young or middle-aged adult presenting with unexplained cough, shortness of breath, or constitutional symptoms, especially among blacks or Scandinavians. Diagnosis relies on three criteria: (1) a compatible clinical and radiologic presentation, (2) pathologic evidence of noncaseating granulomas, and (3) exclusion of other diseases with similar findings, such as infections or malignancy. An early and accurate diagnosis of sarcoidosis remains challenging, because initial presentations may vary, many patients are asymptomatic, and there is no single reliable diagnostic test. Prognosis is variable and depends on epidemiologic factors, mode of onset, initial clinical course, and specific organ involvement. The optimal treatment for sarcoidosis remains unclear, but corticosteroid therapy has been the mainstay of therapy for those with significantly symptomatic or progressive pulmonary disease or serious extrapulmonary disease. Refractory or complex cases may require immunosuppressive therapy. Despite aggressive treatment, some patients may develop life-threatening pulmonary, cardiac, or neurologic complications from severe, progressive disease. End-stage disease may ultimately require lung or heart transplantation for eligible patients.