Intracavitary sonography proved to be advantageous with regard to the T-classification of urinary bladder tumours in comparison with conventional diagnostic methods. Besides the good practicability, the high degree of correspondence between sonography and histopathological findings is emphasized. In 97 patients with urothelial bladder cancer this method yielded 63% correct results. In 32% overstaging was noticed, possible factors of which were exemplified. Part of the sonographic failures can be avoided by means of technical manipulation (gain-modification) together with increasing experience of the examiner. In particular benign bladder disease, which can be sonographically confused with cancer, has to be considered. These cases indicate the need to correlate particular sonographic findings with histopathology.