Between March 1989 and January 1992, 600 cases (636 kidneys) with upper urinary tract stones were treated with ESWL, using a Lithostar. Of these, 78.6% were carried out in our outpatient service, and in the last two years approximately 90% of cases have been treated as outpatient. We evaluated first 500 kidneys, treated with ESWL as outpatient. There were 481 cases involving 500 kidneys (19 bilateral cases). The ages of the 367 men and 114 women ranged from 16 to 77 years. There were 227 kidney stones and 273 ureter stones. Most of the stones were less than 20 mm. The average number of sessions and shock waves for each patient were 1.4 times and 6,988 waves, respectively. While 74% of the patients could be treated in only one session, 9% of them needed 3 sessions or more. Auxiliary measures were needed in 23 cases (D-J stent insertion in 5 cases and ureteral catheterization in 18 cases) and 474 cases (94.8%) were treated by in-situ procedures. At 3 months after treatment, 470 cases were evaluated and the stone-free rates of kidney stones and ureter stones were 70.3% and 84.5%, respectively with an overall stone-free rate of 78.1%. With regard to complications, the rate of the clinic visit because of pain after treatment was observed in 4.6% and higher than 38 degrees C in 2.5%. However, no serious perioperative complications occurred. From these results, outpatient ESWL was considered to be safe and efficient without serious complications.(ABSTRACT TRUNCATED AT 250 WORDS)