Herein we present a case of a 7-month-old baby girl, with left single system ectopic ureter, in whom the ureter was dilated to such an extent that it presented as an abdominal mass. Diagnosis was established by means of computed tomography. Work up was completed with renal scan and micturating cystourethrography. The patient was operated and left nephorureterectomy was performed. Hydroureter has to be considered in differential diagnosis of abdominal mass in an infant.