In 65 patients presenting with mediastinal masses, fine needle aspiration biopsy of the mass was carried out for cytological diagnosis. The procedure was performed with the aid of television-monitored fluoroscopy or computed tomography [CT], resulting in an average positive biopsy rate of 83%. The technique of CT-guided fine needle aspiration biopsy is described and the advantages of this method in diagnosing [neoplastic] mediastinal masses are discussed.