The urographic picture of marked generalized dilatation of the urinary collecting system can present a challenging problem to both the radiologist and the referring clinician. The possible causes are numerous. The frequent occurrence of mild-to-moderate bilateral hydroureter and hydronephrosis during pregnancy or as a consequence of long-standing obstruction due to benign hypertrophy of the prostate is well recognized and needs no further comment. There is also a substantial number of cases, usually in the younger age group, which present as bilateral hydronephrosis and hydroureter but on further investigation demonstrate a structural impairment to bladder emptying. A small group of patients remain, with massive and symmetrical enlargement of the ureters, pelves, and calyces, at times associated with bladder dilatation, in whom careful endoscopic and radiographic investigations fail to provide an explanation for the changes. We have recently observed two such cases in which the radiographic changes were q...