Primitive neuroectodermal tumor/extraosseous Ewing's sarcoma (PNET/EES) is a childhood disease rarely seen in adults. It is a soft tissue tumor, which is often observed in the paraspinal region and lower extremity. We report the case of a 32-year-old man who presented with sudden abdominal pain on the right upper quadrant that was radiated to the right flank. During the operation, a spontaneously ruptured right kidney mass was found. The histopathologic and immunohistochemical characteristics of the excised mass were consistent with PNET/EES. This is the first known reported case of spontaneously ruptured PNET/EES of the kidney with renal vein tumor thrombus. The clinical details and the management of this case are described.