Mediastinoscopy is being used as a diagnostic tool with increasing frequency in this country. In the absence of peripheral nodes, it is a more rewarding procedure than scalene node biopsy in the diagnosis of sarcoidosis. Mediastinoscopy is a better method of detecting lymphatic extension of bronchogenic carcinoma than scalene node biopsy. This technique is useful in the determination of the operability of lung carcinoma. The procedure is usually accomplished with minimal complications.