Purpose: To evaluate prospectively the value of size, shape, margin and density in discriminating between benign and malignant CT screen detected solid non-calcified Pulmonary nodules. Material and methods: This study was institutional review board approved. For this Study 405 participants of the NELSON lung cancer screening trial with 469 indeterminate or potentially malignant solid pulmonary nodules (>50 mm(3)) were selected. The nodules were classified based on size, shape (round, polygonal, irregular) and margin (smooth, lobulated, Spiculated). Mean nodule density and nodule volume were automatically generated by software. Analyses were performed by univariate and multivariate logistic regression. Results were presented as likelihood ratios (LR) with 95% confidence intervals (CI). Receiver operating characteristic analysis was performed for mean density as predictor for lung cancer. Results: Of the 469 nodules, 387 (83%) were between 50 and 500 mm(3), 82 (17%) >500 mm(3), 59 (13%) malignant, 410 (87%) benign. The median size of the nodules was 103 mm(3) (range 50-5486 mm(3)). In multivariate analysis lobulated nodules had LR of 11 compared to smooth; spiculated nodules a LR of 7 compared to smooth; irregular nodules a LR of 6 compared to round and polygonal; volume a LR of 3. The mean nodule CT density did not predict the presence of lung cancer (AUC 0.37, 95% CI 0.32-0.43). Conclusion: In solid non-calcified nodules larger than 50 mm(3), size and to a lesser extent a lobulated or spiculated margin and irregular shape increased the likelihood that a nodule was malignant. Nodule density had no discriminative power. (C) 2007 Elsevier Ireland Ltd. All rights reserved.