We analyzed pre and post enhanced CT scans of eighty two pathologically proven patients among which forty nine cases were pulmonary tuberculosis and thirty three patients, primary lung cancer, who had mediastinal lymphadenopathy, with special attensions to nodal architectures, numbers and locations. The results were asfollows: 1. Lymph nodes abnormality was found in its average number of 1.2 nodes in tuberculosis and 2.8 nodes inprimary lung cancer. 2. The locations of abnormal lymph nodes were 4R(17.5%), 10R(17.5%) and 5(14.0%) in order offrequency in tuberculosis, and 4R(17.6%), 10R(14.3%) and 7(14.3%) in order of frequency in primary lung cancer. 3.In the feature of post enhanced lymph noded, the central low density type was the most frequent in tuberculosis(61.4%). The most frequent type in primary lung cancer was the homogenous type(79.1%). 4. The incidence of lymphnode calcification were as twice in tuberculosis(67.3%) than in primary lung cancer(39.4%) 5. In other findings,parenchymal mass density(78.8% in Ca./12.2% in Tb) and pleural effusion (27.3% in Ca./10.2% in Tb.) were more frequent in primary lung cancer, but parenchymal calcification (27.3% in Ca./49.0% in TB) was more frequent intuberculosis. The cavity formation of primary lung cancer (27.3%) was found to be as the same frequency as intuberculosis(20.4%).