We studied 51 cases of traumatic bladder rupture. Extravasation was noted in 32 cases for which retrograde cystograms were available, including 3 (9 per cent) in which additional infusion of contrast medium was required to demonstrate extravasation. Of the 32 cystograms 4 (13 per cent) showed rupture on the drainage film only. If drainage films and adequate distension of the bladder with contrast medium had been omitted in our study the rate of diagnostic accuracy of the cystogram would have been reduced to 79 per cent. If strict attention is paid to adequate distension of the bladder with contrast material and to obtaining drainage films, diagnostic retrograde cystography for trauma should be almost totally accurate and delays or errors in diagnosis should be rare.