purpose: to assess the efficacy of extracorporeal shockwave lithotripsy (eswl) for ureteral calculi during acute renal colic. materials and methods: from january 2002 to march 2007, 108 patients were treated by eswl for obstructing ureteral stones causing acute renal colic. eswl was performed within 24 hours of the onset of renal colic. results: the mean age of the patients was 39.5 years (11-72 years). male/female ratio was 85/23. mean stone size was 8.45 mm (4-20 mm). they were located in the pelvic (n = 53), iliac (n = 28) or lumbar (n = 27) region. fragmentation after a single session was complete in 56 patients (52%), incomplete in 28 (26%), and absent in 24 (22%). patients presenting incomplete fragmentation underwent a second (n = 28) or even a third session (n = 11). of the 24 patients in whom eswl had no impact on the stone, 21 underwent ureteroscopy, and in one case open ureterolithotomy for a patient with a hard 17 mm stone, while spontaneous passage occurred in two patients with small stones. conclusion: emergency eswl for obstructing ureteral stones has a satisfactory success rate and very low morbidity. the stone-free rate of retreating ureteral calculi with eswl decreases significantly after failed initial treatment. stone size may be the main predictive factor for retreatment. we suggest that no more than 3 treatments should be given for a particular stone due to minimal improvement in the subsequent cumulative treatment success rate.