Translation: Igor Arkadyevich Shaderkin, District Urologist, Seversk Central District Hospital, Department of Surgery. Authors: Department of Urology, Chamran Hospital, Islamic Azad University, Tehran Medical Branch, Hamadan University of Medical Sciences and Shahid Beheshti University of Medical Sciences, Tehran, Iran. Objective: To evaluate the efficacy and safety of acute dilation of the intramural ureter during ureteroscopy using a guidewire technique. Patients and methods: From January 2000 to 2004, 400 ureteroscopies were performed. Of these, 15 men and 5 women (5% of the total number of patients) underwent acute dilation of the intramural ureter using a guidewire technique. The average age of patients undergoing this procedure was 40 years (range, 25–65 years). The authors describe the technique as follows. A guidewire was first inserted into the ureter to a depth of 3-5 cm. A 3 F ureteral catheter was inserted into the ureter through the working channel of the ureteroscope (ureteroscope diameter 8.5-10 F) to a depth of 3-5 cm. The ureteroscope was then gently rotated around its axis and gradually advanced into the ureter. The ureteroscope was positioned between the guidewire (outside) and the ureteral catheter (inside). Advancing the instrument was figuratively reminiscent of a train ride. No double-J stent was inserted postoperatively in any of these patients. The average follow-up period was 25 months (range 6-60 months). Intravenous urography and voiding cystourethrography were performed after 3 months; ultrasound was performed every 3 months during the first year of follow-up and every 2 years thereafter in all 20 patients. Results. Access to the ureter using the described guidewire technique was successful in all patients. Perforations and false passages were not observed in any case. No ureteral strictures or vesicoureteral reflux were detected during any postoperative follow-up examinations. Conclusion: Acute dilation of the intramural ureter using a guidewire technique is a low-cost, safe, easily reproducible, rapid, and predictable method. This technique eliminates the need for balloon dilation of the ureter, significantly saving ureteroscopy time.