Nonneoplastic renal vein thrombosis (RVT) is a clinical dilemma that poses a problem both from a clinical and diagnostic imaging perspective. An accurate noninvasive study to diagnose nonneoplastic RVT would be desirable. Magnetic resonance flow imaging is a noninvasive method of assessing vascular patency and depiction of thrombus. Its use for detection of nonneoplastic RVT is reviewed and our experience illustrated. We reviewed retrospectively the MRI studies in 41 patients evaluated for RVT and correlated them with other imaging studies where possible. Twenty patients had either ultrasound or venography. There were no correlative imaging studies done in 21 patients, 19 of whom had normal MRI, with normal clinical follow-up. In others there was good agreement between MRI and ultrasound in 16 of 19 cases. There were five patients with renal venography, of which the MRI agreed with the results in 3 of 5. Magnetic resonance imaging offers a noninvasive approach to the difficult diagnostic dilemma of RVT.