Thirty patients with partial or total staghorn stones or calculi larger than 30 mm were treated by piezoelectric lithotripsy (PEL) monotherapy using an EDAP LT-01 lithotripter with ultrasound guidance. Nineteen of these patients had pelvic stones; the other 11 had partial (9) or total (2) staghorn stones. All patients first underwent an initial lithotripsy session. No anesthesia or IV sedation was required in any case. If stone fragmentation was achieved during this first session, a double-J stent was inserted before the second lithotripsy session. Prior to the first session, 18 of 30 patients had sterile urine cultures; 12 of 30 presented major distension of the excretory tract. Results were analyzed to determine the factors influencing the outcome of this therapy. Three months after the first session, patients were considered cured if their stones had completely disappeared according to plain abdominal films (14 of 30, 46%). In seven patients (23.3%) fragmentation had occurred but residual fragments remained (1 to 3 fragments less than or equal to 4 mm). No fragmentation was obtained after the first session in nine patients (30.7%) (1 total staghorn stone, 8 pelvic stones). The mean number of treatment sessions was five (range, 1 to 15). Complications occurred in only 10% of patients (3 of 30): two steinstrassen and one acute pyelonephritis. Eighty-three percent of patients without major excretory tract distension and 55% of patients whose initial urine culture was sterile achieved a stone-free state. Therefore the best indications for PEL monotherapy for calculi larger than 30 mm are pelvic stones and partial staghorn stones and no major excretory tract dilatation in patients with sterile initial urine cultures.(ABSTRACT TRUNCATED AT 250 WORDS)