We reviewed the first 100 consecutive patients treated with extracorporeal shock wave lithotripsy (ESWL) at one institution. A total of 115 treatments were delivered to 58 men and 42 women. Patients with calculi of various sizes were treated and compared for (1) length of hospitalization, (2) ancillary procedures, (3) repeat ESWL, (4) obstructive complications, (5) parenteral analgesic requirements, and (6) stone-free rate. Patients were grouped according to calculus length. Group A consisted of 76 patients with calculi totaling less than 3 cm. Group B contained 24 patients with calculi totaling more than 3 cm. In group A, 96% required a single ESWL procedure. Hospitalization averaged two days, and none had obstructive complications; 33% required no parenteral analgesics. In group B, 58% received a single ESWL treatment, whereas 88% required ancillary procedures. Results showed extracorporeal shock wave lithotripsy to be effective treatment of urinary calculi measuring less than 3 cm. Larger calculi required combinations of ESWL with other endourologic treatment.