It is diffidult to distinguish benign from malignant, ulmonary nodule by conventional roentgenologic examination. But CT makes it easier to evaluate adjacent parenchymal invasion, pleural or mediastinal extension, or early metastasis to intra- or extrathoracic lymph node as well s distant organs, although only a solitary peripheral pulmonary nodule is seen on plain radiograph. Authors reviewed CT of 22 cases of histopathologically confirmed primary lung cancer seen as a solitary peripheral pulmonary mass from May 1980 to September 1984 at Dongsan Medical Center, Keimyung University. The results are as follows: 1. The incedence was most common in the 6th decade(36%). Male to female ratio was 10:1 and 2 females all had bronchioloalveolar cell carcinoma. 2. The distributions of histologic cell type were as follows: squamous cell carcinoma 40%, adenocarcinoma, small cell carcinoma, bronchioloalveolar cell carcinoma and unclassified carcinoma 14% in each cases, and adenoid cystic c rcinoma 4%. 3. The computed tomographic findings were as follows: a) Superior and posterior basal segments of both lower lobes were most frequently involved(68%). b) The mean diameter of the mass was 48mm, and most common in the range of 30-49mm in the greatest dimension(46%). c) The mean CT attenuation value was 57 H.U., and most common in the group of 41-70 H.U.(64%). d) Lymph node metastasis was found in 13(59%) of 22 cases, and the involved nodes were as follows: hilar nodes 10 cases, paratracheal nodes 8 cases, subcarinal nodes 7 cases and extrathoracic nodes 3 cases. In 2 of 3 cases with small cell carcinoma, diffuse multiple lymph nodes were involved. e) Distant metastasis was seen relatively early in 3 cases: cerebral metastasis in 1 case of squamous cell carcinoma, right adrenal metastasis without intrathoracic lymph node metastasis or invasion of adjacent structures in 1 case of bronchioloalveolar cell carcinoma, and liver and bone metastases in 1 case of unclassified carci oma. f) Adjacent pleural or mediastinal invasion was found in 7 cases(32%): pleural invasion alsong chest wall in 4 cases, and invasion of adjacent mediastinal pleura in 3 caes of 2 squmous cell carcinoma and 1 unclassified carcinoma. g) Calcifications within the mass were found in 5 caes(23%), and most common in squamous cell carcinoma(3 caes). In all cases, a few granular calcifications were seen along the peripheral margin of the mass. h) Tumor necrosis was seen in 4 cases(18%), and 3 cases were squamous cell carcinoma, and one of them showed irregular central cavitation. i) The margins of tumor were irregularly lobulated with radiating spiculations in all except one of adenoid cystic carcinoma, which revealed oval shaped, smooth clear margin. j) In 9(41%) of 22 cases, some enlargement of pulmonary vessels with perivascular linear infiltrations were found in the adjacent lung parenchymes of the mass, which were thought to be retrograde perivascular lymphangitic spread along pulmon ry vessels.