The role of ultrasonographic examination of the bladder has been retrospectively evaluated in 12 patients with hemorrhagic cystitis occurring after BMT. Three sonographic patterns of bladder abnormalities have been observed: type 1, circumscribed thickening of the wall protruding into the lumen (4 patients); type 2, diffuse thickening of the wall (3 patients); type 3, intraluminal lobulated bulky mass reducing the capacity (5 patients). Sonographic follow-up showed a progressive trend of bladder abnormalities: type 3 lesions were always preceded by type 1 or type 2 abnormalities. In 10 of 12 patients the cystoscopic findings proved the correlation between the sonographic aspects and the progressive stages of bladder wall damage. Patients were treated initially by hyperhydration and blood products transfusions in order to stop hematuria. The median duration of bleeding was significantly longer (p < 0.01) in patients showing type 3 lesions (90 days) than in the combined groups with types 1 or 2 lesions (14 days). All 5 patients with type 3 abnormalities failed treatment and required endoscopic removal of clots; hemorrhagic cystitis was the major cause of death in 3 patients in this group. Ultrasonography may therefore be considered an accurate investigation for assessing the extent of bladder damage and monitoring the effectiveness of treatment for this complication.