Duplication of the ureters is a common anomaly and is frequently encountered by radiologists. Duplication may be either complete or incomplete and is often accompanied by various complications. Incomplete duplication is most often associated with ureteroureteral reflux or ureteropelvic junction obstruction of the lower pole of the kidney. Complete duplication is most often associated with vesicoureteral reflux, ectopic ureterocele, or ectopic ureteral insertion, all of which are more common in girls than in boys. Vesicoureteral reflux affects the lower pole and can be outgrown, as in nonduplicated systems. Ectopic ureterocele and ectopic ureteral insertion affect the upper pole. The ectopic ureterocele produces a filling defect of variable size in the bladder; it can be identified with contrast material studies or ultrasound. Ectopic ureters may function poorly, be difficult to detect, and cause enuresis in girls. A fourth complication, ureteropelvic junction obstruction, occurs only in the lower pole and is seen in more boys than girls. Anatomic variants or anomalies as well as suboptimal imaging techniques can either simulate or obscure duplication, making diagnosis difficult. However, familiarity with the embryology of duplication and an awareness of the potential pitfalls of excretory urography and voiding cystourethrography will foster an understanding of the varied appearances and associated complications of both incomplete and complete duplication.