A case of retrocaval ureter in which the diagnosis was made preoperatively has been described. The condition should be suspected in any unexplained right hydronephrosis, for there are no pathognomonic signs or symptoms. The preoperative diagnosis depends upon the demonstration of an abnormal course of the ureter by intravenous and retrograde pyelography. For an absolutely positive diagnosis, however, simultaneous catheterization of the vena cava and of the ureter, along with stereoscopic views, should probably be carried out in all cases. If surgical treatment is necessary and nephrectomy can be avoided, the preferred methods of treatment consist of either section and re-anastomosis of the ureter or section and re-anastomosis of the vena cava.