Purpose : The purpose of this study was to compare the diagnostic accuracies of chest radiographs and chest CTin the diagnosis of a solitary pulmonary nodule(SPN), and to determine the role of CT and CT findings which aid inthe differential diagnosis of nodules. Materials and Methods : A retrospective study was done on 54 patients inwhom SPN was found on chest radiographs and chest CT was carried out. The study involved 25 benign and 29malignant nodules, confirmed histopathologically and clinically. Chest radiographs and CT scans were reviewedseparately in randomized order by two chest radiologists who for each film listed the three most likely diagnosesin descending order. The radiologists recorded the confidence value of the most probable diagnosis, and also themarginal and internal characteristics of nodules and their size, as nodules seen on chest CT scans. Results :Diagnostic rates in the differential diagnosis of benign and malignant nodules were 65.7% by radiography and 77.8% by CT. Correct first-choice diagnosis was by radiography in 30.6 % of cases, and by CT in 41.7%. Usingradiographs, and the correct diagnosis was among the top-three choices in 61.1% of cases ; with CT, thecorresponding figure was 76.8%. Overall, a confident diagnosis was reached more often with the CT(41.7%) than withthe chest radiograph(21.4%) ; diagnaotic accuracy was 60.0% and 52.2%, respectively. CT findings which imply abenign nodule include smooth margins and diffuse internal calcifications, whereas marginal lobulations, air-bronchograms, internal low density without cavitation, eccentric calcifications, and large size suggestmalignancy. We faund that CT findings such as well-defined margins, spiculations, pleural tail or internalhomogeneity did not contribute in the differentiation between benign and malignant nodules. Conclusion : CT issuperior to chest radiography in the differential diagnosis of the solitary pulmonary nodule. Using CT, diagnosiswas accurate and made with a high level of confidence, especially with the application of CT findings which aid inthe differential diagnosis of nodules.