During 10 months at our hospital, 413 patients underwent extracorporeal shock-wave lithotripsy (ESWL). The occurrence of complications was examined in the 126 (30.5%) of these patients who had sterile urine before the procedure and who had neither indwelling catheters nor stents. No patient received prophylactic antibiotics. After ESWL, nine patients (7%) developed bacteriuria, which was usually transient and required no therapy. Seven of the nine cases developed within 2 weeks of ESWL. In no case did other complications follow bacteriuria. Patients in whom bacteriuria was suspected because of fever all proved to have sterile urine. Our results indicate that patients whose urine is sterile before ESWL do not need antimicrobial prophylaxis.