The unusual combination of reflux and obstruction as seen in 8 of a series of 40 unduplicated ureters reimplanted for reflux is presented, with particular reference to the mechanical obstructing factors which can be demonstrated. These involve the extravesical rather than the intravesical ureter so that separate pathologic mechanisms for obstruction and reflux must be postulated. This unusual obstruction/reflux combination appears to be more common than is generally recognized, and the need for its early recognition and surgical correction contrasts with the less urgent indications for operative intervention in ureteric reflux alone.