The transthoracic fine needle biopsy is a very efficient method in the differential diagnosis of pathological intraplumonary or mediastinal processes. If the material is representative (out of 918 patients in 71.6 percent), the cytological examination produced a correct result in 93.4 percent (in 614 cases out of 658). In 428 cases of intrathoracic malignant diseases an accurate diagnosis was established in 94.6 percent, and out of the patients with a benign inflammatory disease we could give frequently a hint at the definitive diagnosis in addition with other clinical and paraclinical dates. The false positive rate was 1.3 percent, and in 5.3 percent a false negative result was obtained. Our rate of complications was 16.7 percent.