Forty-two patients with carcinoma of the bladder were examined by intravesical and transcutaneous sonography, as well as by computed tomography, in order to determine their T-classification. None of these methods permitted a distinction between T2 and T3a as recommended by the UICC (1978), with any degree of certainty. Intravesical sonography is best for defining superficial tumours. Transcutaneous sonography has proved satisfactory for differentiating muscle-infiltrating from extravesical tumours. Computed tomography shows infiltration of tumour into the perivesical fat and into neighbouring organs; infiltration of tumour into the prostate cannot always be demonstrated.