Urinary incontinence in girls is very common, usually presenting as intermittent, frequent urinary dribbling due to detrusor instability. Rarely, continuous urinary dribbling is caused by a dysplastic, poorly functioning moiety of a duplex kidney, or a unilateral dysplastic kidney draining into a ureter that exits ectopically to the vagina or distal urethra.1-4Typically, the diagnosis is made after a long delay.2-4This is partly because the dribbling pattern is not always easy to ascertain,3 but mainly because it may be difficult to confirm the diagnosis preoperatively by examination of the genitalia,2 ,4 or using various imaging techniques.1-4 We present a girl in whom the diagnosis was confirmed by chemical analysis of urine collected after the administration of desmopressin acetate.