47 children diagnosed as having obstructed or non-refluxing, non-obstructed, primary mega-ureters were followed up by questionnaire. 2 patients had developed renal failure over 20 years, the remainder were free of urinary tract infection or hypertension. 21 of these patients were followed up with clearance and differential renal function studies. All but 4 kidneys associated with operated mega-ureters at long term follow-up had good function.