We report 8 patients with urolithiasis in a duplex system. These patients (7 males and 1 female) underwent 16 extracorporeal shock wave lithotripsy (ESWL) treatments. Five had renal and 3 had ureteral stones. The mean stone size was 21 mm (12-54 mm). Five patients had incomplete and 3 had complete duplication, of which one had an associated horseshoe kidney. Retrograde ureteropyelography was done in all the patients and in 7 a JJ stent was inserted. The JJ stent could not be inserted in 1 patient with incomplete duplication and retrograde catheterization with saline infusion was used as an auxiliary procedure. One patient with complete duplication had stones in both the ipsilateral ureters with a stone bulk of 54 mm and required two JJ stents. Only 1 paediatric patient required general anaesthesia. The 3-month stone-free rate was 100%.