The literature with regard to roentgenologically demonstrable calcification of urinary bladder tumors has been surveyed, and 3 additional cases in which this phenomenon occurred have been reported. The extremely rare finding of a primary osteogenic sarcoma of the urinary bladder and a brief review of the related literature have been presented. The finding of unusual calcific densities in the region of the urinary bladder within a space-occupying lesion probably is an ominous sign.