Inflammatory myofibroblastic tumor (IMT) is a rare disease of inflammatory and spindle cell proliferative lesions in multiple sites. Most frequently reported in the lungs, a variety of extrapulmonary sites have been described. We report the first case of IMT causing renal failure by massive bilateral renal infiltration. Renal function continued to deteriorate (peak serum creatinine level, 8.4 mg/dL) despite placement of a ureteral stent. The kidneys were diffusely enlarged on computed tomographic (CT) scan. Renal biopsy showed myofibroblastic proliferation and inflammatory infiltration. Renal failure responded favorably over weeks to corticosteroid therapy (serum creatinine level, 2.8 mg/dL) with a marked reduction in bilateral renal enlargement by CT scan.