One hundred and fourty patients with a primary lung neoplasm underwent transmission computed tomography (TCT) for staging prior to therapy. TCT results were compared with the post-operative T- and N-stage. The preoperative TCT examination correctly classified 70% of all tumors. 73% of T1, 63% of T2 and 74% of T3 tumors did not require restaging after surgery. TCT correctly staged 80% of the patients with respect to the N-stage. Ninety-seven percent of the patients with N0, 42% with N1 and 79% with N2 tumors were correctly classified. Serious over- and understaging was observed in patients with centrally located bronchogenic carcinoma. This was due to the difficulty of distinguishing tumor tissue from enlarged lymph nodes and atelectasis.