Primary leiomyosarcomas of the retroperitoneum are rare tumors, the vast majority of which are malignant. Prognosis is largely dependent upon adequacy of surgical resection. Magnetic resonance imaging (MRI) is ideally suited to the evaluation of these neoplasms because of multiplanar imaging capability, inherent signal intensity differences of tissues, and flow-void, flow enhancement techniques to assess vessel patency. Recent advances which include fat suppression, suspended respiration sequences, and Gadolinium enhancement, have further improved image quality. Accurate pre-operative assessment of tumors is possible with MRI.