The primary retroperitoneal tumors form a rare and diverse group of neoplasms, the origin of which is independent of the various retroperitoneal organs and unrelated to systemic diseases, such as lymphomas, lymphadenopathy, or metastases. Radiologic investigation, mainly cross-sectional imaging and, to a lesser extent, angiography is essential in the diagnosis and management of these tumors. The radiologist often is challenged to identify the origin and specific tissue composition of the imaged neoplasms. When the radiologic findings are combined with patient information and clinical data, the correct diagnosis may be made in many cases. Imaging-guided percutaneous needle biopsy further enhances the diagnostic yield of the various imaging modalities by establishing the diagnosis without the need for exploration.