Introduction and Objectives:Urinary infection behind an obstruction is a urologic emergency.Patients with urosepsis associated with urinary tract calculi occasionally require drainage.Clinicians are also interested in the severity of ureteral obstruction.Secondary signs of obstruction are necessary to confirm the diagnosis and obtain an idea concerning the severity of obstruction.On contrast-enhanced CT, the typical findings of severe obstruction include delayed calyceal opacification.We investigated the characteristics of patients with acute obstructive pyelonephritis and evaluated the diagnostic relevance of excretory phase CT.