Eosinophilic cystitis is a rare bladder lesion which usually presents with nonspecific symptoms including recurrent hematuria, dysuria and frequency. We report a case that developed after radical prostatectomy. The lower urinary tract symptoms persisted despite of various antibiotics treatments. Eventually, the disease progressed to involve both ureters and bilateral hy-dronephrosis ensued. The ureteral obstruction was not improved even after ileal conduit urinary diversion but finally responded to steroidal therapy. Although eosinophilic cystitis is reported to be probably of immunological nature, trauma and bladder surgery have also been implicated as possible etiologic factors. Since the diagnosis can only be made pathologically, a successful management of this disease required awareness and alertness of both urologists and pathologists.