During the last 10 years we have treated 24 newborn and young infants (27 ureters) in whom the diagnosis of primary obstructed megaureter was established by diuresis-enhanced radionuclide renography and/or by antegrade pressure flow studies (Whitaker test). Temporary uretero-cutaneostomy was performed immediately after diagnosis. After 1 year a second modified Whitaker test showed normal passage of the contrast medium into the bladder in 23 ureters. In only 4 ureters did obstruction persist and uretero-cystoneostomy was performed. Ureterocystoneostomy was also performed on 8 ureters without obstruction but with persistent vesicoureteric reflux, ectopic ureter or diverticula. In 11 patients a temporary uretero-cutaneostomy was closed without corrective surgery at the vesicoureteric junction. Temporary uretero-cutaneostomy is a safe and effective therapy in primary obstructed megaureter in newborns. Spontaneous relief of obstruction appears to be possible in primary obstructed megaureter.