In order to prospectively assess various parameters of diffusion weighted imaging (DWI) in differential diagnosis of benign and malignant solitary pulmonary nodules (SPNs), 58 patients (40 men and 18 women, and mean age of 48.1 +/- 10.4 years old) with SPNs undergoing conventional MR, DWI using b=500 s/mm(2) on a 1.5T MR scanner, were studied. Various DWI parameters [apparent diffusion coefficient (ADC), lesion-tospinal cord signal intensity ratio (LSR), signal intensity (SI) score] were calculated and compared between malignant and benign SPNs groups. A receiver operating characteristic (ROC) curve analysis was employed to compare the diagnostic capabilities of all the parameters for discrimination between benign and malignant SPNs. The results showed that there were 42 malignant and 16 benign SPNs. The ADC was significantly lower in malignant SPNs (1.40 +/- 0.44)x10(-3) mm(2)/s than in benign SPNs (1.81 +/- 0.58)x10(-3) mm(2)/s. The LSR and SI scores were significantly increased in malignant SPNs (0.90 +/- 0.37 and 2.8 +/- 1.2) as compared with those in benign SPNs (0.68 +/- 0.39 and 2.2 +/- 1.2). The area under the ROC curves (AUC) of all parameters was not significantly different between malignant SPNs and benign SPNs. It was suggested that as three reported parameters for DWI, ADC, LSR and SI scores are all feasible for discrimination of malignant and benign SPNs. The three parameters have equal diagnostic performance.