Purpose : To evaluate the CT findings of pleural dissemination in primary lung cancer and the limitations ofCT scanning in detecting pleural dissemination in primary lung cancer. Materials and Methods : Primary lung cancerwith pleural dissemination was diagnosed in 68 patients and confirmed by pleural biopsy, cytology and surgery, andthese cases were the subject of this study. Adenocarcinoma accounted for 49, squamous cell carcinoma for 13 andsmall cell carcinoma for six. Eight CT features, namely the amount of pleural effusion, the contour, extent andlocation of pleural thickening, the shortest distance between pleura and mass, pleural calcification, pleural tailsign and the extent of extrapleural fat proliferation, were evaluated. Results : Pleural effusion was noted in 51of 68 patients(75%), though in most cases(70%), the amount of this was small. Among 42 patients(62%) in whomthickened pleura, were noted, pleural thickening was thin and irregular in 22(52%), thick and irregular in16(38%), and thin and regular in 4(10%). The extent of pleural thickening was multifocal in 22 patients(52%),diffuse in 16(38%), and circumferential and single in two(5%). Pleural thickening was more frequently noted at theposterior than the anterior pleura. Pleural abutting was seen in 53 patients(78%). In ten patients(15%), chest CTscans revealed no perceptible pleural abnormalities. Conclusion : If in primary lung cancer, the primary lung masscontacts the pleura, and if pleural thickening, even when slight, shows marginal irregularity, pleuraldissemination should be considered. Although CT scanning is very useful for the detection of pleural disseminationin primary lung cancer, about 15% of patients showed no perceptible pleural abnormalities. Other diagnosticmodalities such as thoracoscopy are mandatory for the correct diagnosis of pleural dissemination in primary lungcancer.