Abstract Background: Diffusion-weighted imaging (DWI) is a non-invasive method that is based on the movement of water molecules across tissues. DWI and the apparent diffusion coefficient (ADC) may provide additional information to that obtained from conventional MRI. DWI can contribute to differentiate between active and chronic (inactive) RPF as well as between benign RPF and malignant neoplasms with RPF morphology. Aim of Study: To evaluate diffusion-weighted imaging (DWI) features and signal intensity values at T2-weighted magnetic resonance (MR) imaging for differential diagnosis of benign retroperitoneal fibrosis (RPF) and plaque-like retroperitoneal malignant neoplasms. Patients and Methods: Thirty-eight patients (mean age 56.50±11.125 years; range 29-76 years, 24 males and 14 females) with plaque-like confluent retroperitoneal soft-tissue masses were divided into three groups: group I, 16 patients with malignant RPF and retroperitoneal malignant neoplasm; group II, 10 patients with active RPF; and group III, 12 patients with chronic RPF. MRI protocol included T1 -weighted (non-enhanced and contrast-enhanced), T2-weighted, and DWI (b=1000 sec/mm2) images and apparent diffusion coef-ficient (ADC) values. Results: Overall sensitivity, specificity, and positive and negative predictive values as well as diagnostic accuracy when using ADC values were (90%, 91.7%, 90%, 91.7%, and 90.9%, respectively) in differentiating between active and chronic RPF. While, overall sensitivity, specificity, and positive and negative predictive values as well as diagnostic accuracy when using ADC values were (81.8%, 75%, 81.8%, 75%, and 79%, respectively) in differentiating between malignant from benign cases. Conclusion: DWI can contribute to differential diagnosis of active from chronic RPF and benign RPF from malignant neoplasms with RPF morphology. ADC of chronic RPF was higher than that for active RPF or malignant group. Lesions in the malignant group and active RPF group had similar enhancement patterns, while those in the chronic RPF group demonstrated less enhancement. Signal intensity values on T2-weighted images were not useful for differentiating these conditions.