Leukoplakia of the renal pelvis can be diagnosed preoperatively. Yet in only six of the reported cases has the diagnosis been made before surgery. This lesion is premalignant, and the treatment in the unilateral case is nephrectomy. All three of the cases here reported were diagnosed before surgery by means of the history, suspicious findings of pyelographic examination, and cell block studies of the urine. The most dramatic symptom may be flank pain associated with the passage of "sheets" from the shedding lesion. Pyelograms typically show linear striations or mottling which should arouse suspicion. The presence of keratin or keratinized squamous cells in the urine cell block study is pathognomonic. The treatment of unilateral leukoplakia of the renal pelvis in these cases was nephrectomy. This was curative, as shown when the three patients were reexamined four to five years later.