One hundred and twenty patients with large renal calculi (greater than 3 cm), who had not undergone previous stone-debulking procedures, were treated with extracorporeal shock wave lithotripsy (ESWL) monotherapy using a Dornier HM3 lithotripter. Stones were divided into four categories according to Rocco's classification: 20 C2, 25 C3, 51 C4 and 24 C5. Repeated treatments were necessary in 13 patients, while planned two-stage treatments were performed in 8. Pretreatment adjunctive endourological maneuvers (except for the placement of ureteral stents for visualization of 37 contrast-negative stones) were used in 16 cases (13.3%) and posttreatment maneuvers in 20 (16.6%). Open surgery was necessary in 6 patients, including one nephrectomy. Complete elimination of all concrements was documented in 74 patients (61.6%): 63 within 3 months and 11 within 6-12 months. The stone-free rates for different categories were: 80% for C2, 64% for C3, 58.8% for C4 and 50% for C5. The stone-free rate for contrast-negative calculi was 83.7% (31/37), and for radiopaque ones 51.8% (43/83) (p less than 0.001). It is concluded that ESWL monotherapy is an adequate treatment choice for some categories of large radiopaque stones and for all radiolucent ones.