OBJECTIVE We determined the efficacy of ureteroscopic treatment of upper urinary tract transitional cell carcinoma. METHODS Of 92 patients diagnosed with upper urinary tract transitional cell carcinoma at our institution from 1985 to 1995, 38 (41 kidneys) underwent ureteroscopic treatment and followup. Semirigid and flexible ureteroscopes were used to examine the collecting system. Tumors were biopsied, and treated with fulguration, the neodymium:YAG laser and/or the holmium:YAG laser. Patients were treated every 6 to 12 weeks until tumor-free and then followed on a strict endoscopic protocol. RESULTS Mean and median followup was 35.1 and 26 months, respectively (range 3 to 116). Grading of ureteroscopic biopsies was possible in 40 of 41 cases. Initial grading of tumors was low (grade 1 or 1 to 2) in 21 kidneys, grade 2 in 14 and grade 3 in 5. Of 41 kidneys 28 (68%) were documented as tumor-free ureteroscopically at some time following treatment, including 8 (29%) with subsequent recurrences that were treated endoscopically and 24 (86%) with no evidence of disease at the most recent followup. No patient to date has had progression of disease during endoscopic followup. High tumor grade, size and multifocality were significantly associated with tumor persistence and recurrence. Location in the kidney versus ureter was not a significant prognostic factor. Of the recurrent tumors 75% were not identified radiographically but were only discovered endoscopically. Two of 8 kidneys removed after endoscopic treatment had no tumor stage (pT0). CONCLUSIONS Endoscopic treatment of upper urinary tract transitional cell carcinoma is a reasonable method to treat carefully select patients based on strict indications. Complete endoscopic followup at regular intervals is essential to rule out recurrences.