Between January and December 1989, 123 patients with distal ureteral stones were treated with in situ extracorporeal shockwave lithotripsy (ESWL) using a modified HM3 Dornier lithotriptor. One hundred and three patients (83.7%) were stone-free, 20 patients (16.3%) had small residual stones (< 1 mm2) that passed spontaneously. In situ ESWL treatment alone was successful in 88 of the 103 stone-free patients (85.4%). Fifty-six (54.4%) needed 1 ESWL session, 26 (25.2%) needed 2 ESWL sessions. Nineteen of the 123 patients (15.4%) needed auxiliary endourological measures. The results of ESWL treatment were correlated to pretherapeutically identified parameters such as stone size, radiopacity, outer contour, shape, inner structure, biochemical analysis of the stones and grade of dilatation of the upper urinary tract. The results prove that size (> or = 75 mm2), radiopacity and grade of dilatation have a direct correlation to the difficulty to disintegrate ureteral stones.