PURPOSE: The aim of our study was to evaluate the usefulness of high-resolution CT scans in addition tohelical CT for characterizing a solitary pulmonary nodule. MATERIALS AND METHODS: Our study included 49 patientswith a solitary pulmonary nodule ; in each patient this was evaluated by both additional high-resolution CT andhelical scanning. Images were evaluated by three independent observers, each of whom read them twice : initiallywith helical CT images only and then with helical images plus high-resolution CT images. After analysis, theobservers recorded the following : histologic diagnosis, benignancy or malignancy of a nodule, and confidence intheir diagnosis (three scales). RESULTS: In differentiating benign and malignant nodules, the accuracy of helicalscans only was 75% (110/147 readings) whereas that of helical plus high-resolution CT scans was 82% (121/147readings) (p=0.001). Correct histologic diagnosis was made in 47% of cases (69/147 readings) when helical scansonly had been evaluated and in 48% of cases (71/147 readings) for which both helical and high-resolotion CT scanswere available (p=0.815). Diagnosis was more often highly confident on the basis of additional high-resolution CTscans (25%) than helical scans only (5%) (p=0.001) . CONCLUSION: By enhancing differential diagnosticaccuracy between benign and malignant nodules and by increasing confidence in the histologic diagnosis of apulmonary nodule, additional high-resolution CT scans are valuable for the evaluation of a solitary pulmonarynodule.