The clinical records of 44 children (34 girls and 10 boys) with ureteroceles, seen at the Squier Urological Clinic during a period of 27 years, have been reviewed and the findings tabulated. Of the 44 cases, 38 were found clinically among some 3,800 new pediatric urologic admissions, an incidence of 1 in every 100 new pediatric urologic patients. The other six cases were found incidentally at necropsy at the Babies Hospital, among 3,200 consecutive necropsies, i.e., one in every 500 general pediatric necropsies. Among the 38 clinical cases of ureteroceles 85% had severe dilatation of one or more upper urinary tract units, 25% of which had also evidence of bladder-neck obstruction caused by the ureterocele. In the remaining 15%, the dilatation was confined to one upper urinary tract unit and was minimal or mild. As expected, large ureteroceles were present in those patients with unilateral or bilateral duplication of the upper urinary tract, and caused severe hydroureteronephrosis, while small ureteroceles were usually seen in children with single upper tracts, and produced minimal or mild ureteropyelic dilatation. Unilateral or bilateral duplication of the upper urinary tracts was also present in 75% of the 38 cases and in 90% of those who had large ureteroceles. In all children with duplicated urinary tract who had ureteroceles, the latter were always found involving the lower ureteral ostium; i.e., the one which drained the upper kidney. There was no characteristic clinical picture caused by this condition, but fever, pyuria and recurrent abdominal pain were usually present. Urography was helpful in establishing a correct diagnosis of ureterocele in about 50% of all cases irrespective of the status of the ureterocele and quality of the film. Cystoscopy was only done whenever the diagnosis was not previously established by urography on in difficult situations such as those seen in collapsed ureteroceles. In this latter group the cystoscopic findings were bizarre and at times misleading. Transcystoscopic excision of the ureterocele was carried out in many cases but with good results only in those children with small uneteroceles and minimal to mild dilatation of the upper urinary tract. Nephrectomy or heminephroureterectomy was the treatment of choice in children with large ureteroceles and severely dilated upper urinary tracts. At times, multistaged procedures were necessary in order to achieve a satisfactory result, the initial step being a simple cystoscopic fulguration or a suprapubic excision, or uncapping of the ureterocele. Whenever the general condition of the child was satisfactory, the treatment consisted of attempts at repair of the anomaly, when feasible, or radical excision not only of the uneterocele but also of the involved renoureteral unit or units if the remaining kidney was considered sufficient to support a useful life. Finally, a prolonged course with antibiotics and chemotherapeutic agents usually followed surgery, in order to control the concomitant infection of the urinary tract. Ureteroceles in children were found to be apt to produce serious hydrodynamic disturbances of the upper urinary tracts and sometimes obstruction of the bladder neck. Furthermore, bizarre clinical syndromes, misleading cystoscopic findings and confusing urographic pictures were present in about 30% of the 38 clinical cases of ureterocele in children seen at the Squier Urological Clinic and described in this report. In these cases the correct diagnosis was initially overlooked or delayed, adequate treatment postponed or incompletely carried out, and the results obtained were poor. On the other hand, satisfactory result were usually achieved in the remaining 70% of the cases in which a correct diagnosis was established early and adequate treatment instituted. For these reasons, familiarization with the various clinical, cystoscopic and urographic findings encountered in children with ureterocele is important in order to bring about early diagnosis and treatment of this condition.