Thirty-two consecutive patients with mediastinal lesions suggestive of bronchogenic carcinoma underwent transbronchial needle aspiration. Eighteen of 20 patients (90 percent) with proved bronchogenic carcinoma had malignant cytology specimens or tissue fragments. Of 12 patients with normal cytology specimens, six were subsequently proved to have nonneoplastic disease. Transbronchial needle aspiration appears to offer a sensitive and specific alternative to more invasive surgical techniques used in the diagnosis of malignancies with mediastinal involvement.