Enterovesical fistulae are difficult to demonstrate by conventional radiographic methods. Computed tomography (CT), a sensitive, noninvasive method of documenting the presence of such fistulae, is unique in its ability to outline the extravesical component of the primary disease process. Twenty enterovesical fistulae identified by CT were caused by diverticulitis (nine), carcinoma of the rectosigmoid (two), Crohn disease (three), gynecologic tumors (two), bladder cancer (one), cecal carcinoma (one), prostatic neoplasia (one), and appendiceal abscess (one). The CT findings included intravesical air (90%), passage of orally or rectally administered contrast medium into the bladder (20%), focal bladder-wall thickening (90%), thickening of adjacent bowel wall (85%), and an extraluminal mass that often contained air (75%). The fistulae secondary to diverticulitis, rectosigmoid neoplasms, carcinoma of the bladder, and uterine tumors involved the left and/or posterior aspects of the bladder. Those form Crohn disease of the terminal ileum or cecal and appendiceal lesions implicated the right lateral or anterior aspects of the bladder. CT proved to be an important new method in the diagnosis of enterovesical fistulae.