Renal ultrasound scan, circulating creatinine and calcium, and the urinary calcium excretion rate were investigated in 57 patients with clinically and genetically typical Williams-Beuren syndrome (25 female and 32 male subjects, aged from 1.0 year to 23 years, median 8.5 years) on regular follow up at our institution. Twenty-three unilateral abnormalities were detected in 20 patients: pelvic dilatation ( n=6), renal hypoplasia ( n=5), isolated renal cyst ( n=3), kidney surface irregularity ( n=3), kidney duplication ( n=2), renal agenesis ( n=1), megaureter ( n=1), pelvic kidney dystopia ( n=1), and renal stone ( n=1). Both infantile hypercalcemia and nephrocalcinosis was absent in the 57 patients. Mild hypercalcemia was noted in 1 and mild hypercalciuria in 2 patients after the 1st year of life. In conclusion, the study indicates the frequent occurrence of intrinsic renal tract abnormalities detected by ultrasonography in Williams-Beuren syndrome. However, the study does not confirm the importance given in the past to the occurrence of hypercalcemia and hypercalciuria.