We studied 200 postmortem ureters from 100 adult men to test the hypotheses that ureteral pseudodiverticula (UPD) are more prevalent than clinically recognized, that UPD are secondary to chronic inflammations, and that they are associated with uroepithelial neoplasm. The ureters were inflated with 10% formaldehyde and fixed for 24 hours. One hundred sixteen ureters were drained and refilled with 25% diatrizoate sodium meglumine and radiographed before gross and microscopic pathologic examination. No radiographs of the remaining 84 ureters were obtained. UPD were identified pathologically in 11%. None of these patients had a history of upper urinary tract disease. UPD were smaller than those reported clinically and invariably were associated with focal microscopic ureteritis cystica and glandularis in ureters otherwise free of histologic abnormality. UPD displayed mild benign mucosal hyperplasia with invagination in the subepithelial connective tissue as well as impression and sometimes thinning of the muscularis propria but without penetration. No mucosal atypia or malignancy was seen. We postulate that UPD represent a proliferative response to focal inflammation resulting in intramural invasion producing elevation and thinning of the ureteral wall. Continued focal inflammation may be sustained by local urine stasis. Enlargement to clinically detectable size may be enhanced by more generalized disease such as clinical infection, stone, or obstruction.