puncture, 1 while others offer nonoperative treatment with antibiotic prophylaxis. We report on an infant with bilateral, nonobstructing nonrefluxing ureteroceles treated nonoperatively with subsequent development of small calculi in the left ureterocele. CASE REPORT A 6-week-old male with bilateral grade 2 prenatal hydroureteronephrosis had bilateral single system ureteroceles on postnatal sonography (fig. 1, A). The parents reported no history of illness and the patient was on no medication. Antibiotic prophylaxis, including 10 mg./kg. amoxicillin daily, was initiated. A cyclic voiding cystourethrogram confirmed the diagnosis of bilateral ureteroceles, and revealed an otherwise normal bladder and urethra without reflux. Furosemide renography showed bilateral hydroureteronephrosis with homogeneous distribution of radiopharmaceutical from the cortex of each kidney with differential function of 46% and 54% from the right and left kidney, respectively. There was prompt emptying of the renal pelves after furosemide administration. The half-time washout was 6 minutes for the right and 9 for the left kidney, and percentage washout was 81% and 77%, respectively. The patient was continued on antibiotic prophylaxis without incident and evaluated at, ages 4 and 6 months with renal sonography and urinalysis. All urinalyses were negative, and the sonograms revealed stable hydroureteronephrosis, no renal abnormalities and maintenance of good corticomedullary differentiation. However, renal sonography at age 8 months revealed the interval development of 3 small stones in the left ureterocele (fig. 1, B). The patient subsequently underwent transurethral incision of the ureteroceles and extraction of the left ureteral stones. He tolerated the procedure well and was continued on antibiotic prophylaxis. Repeat sonography 1 month postoperatively showed no hydronephrosis or calculi and redundant incised ureterocele tissue (fig. 2). Chemical analysis of the stones revealed 80% calcium oxalate dihydrate, 10% ammonium magnesium phosphate hexahydrate and 10% calcium oxalate monohydrate. A voiding cystourethrogram at age 14 months revealed vesicoureteral reflux grade III on the left side and no reflux on the right. The patient remains on prophylactic antibiotics and has not had a urinary tract infection postoperatively.