The aim of the study was to analyse factors affecting the success rate of extracorporeal shock wave lithotripsy (ESWL) in children with renal calculi. We performed a retrospective analysis reviewing records of 85 (40 female, 45 male) children (89 renal units) subjected to ESWL for treatment of renal calculi during 1990-2005 in our department. As 4 patients had bilateral calculi and 19 children (21 renal units) had renal stones at more than one different site, each location was analysed separately for convenience. The mean age of the patients was 10.3 +/- 4.6 (2-16) years. The stone-free rates for renal pelvis, lower, middle and upper caliceal calculi were 70, 62, 50 and 73%, respectively. A higher rate (33%) of insignificant fragments (<= 4 mm) was noted for lower pole calculi. Increased stone diameter (P=0.0001) and burden (P=0.04) were found as the most significant factors that adversely affect the stone-free rate for pelvis renalis calculi, whereas an acutely oriented infundibulum and/or a long lower infundibulum (P=0.005) were unfavourable factors for clearance of lower caliceal stones. The stone-free rate in children with multiple calculi was 48%, while 29% of the renal units had retained fragments. ESWL is a good initial option for treatment of most of the renal calculi < 2 cm except in the presence of unfavourable lower caliceal anatomy. Increased stone burden, multiple stones, staghorn calculi, narrow lower infundibulopelvic angle and long lower infundibulum are factors that adversely affect the clearance rate.