PURPOSE: To compare the role and clinical usefulness of virtual and convetional cys-t o s c o py in patientswith known bladder tumors. MATERIALS AND METHODS: S eventeen patients with a known bladder tumor underwentvirtual and conventional cystoscopy. As a result of conventional cystoscopy and s u r g e r y, 32 tumors weredetected. Prior to examination, each patient lay supine on the CT table, and the urinary bladder was catheterized,drained of all urine, and inflated with air. Spiral CT of the pelvis was then performed. CT data were transferredto a separate workstation and three-dimensional and virtual cystoscopic images were reconstructed. The latter wereinterpreted by two radiologists, who recorded the number, size, morphology, and exact location of the massesobserve d. The results of virtual CT cystoscopy were correlated with conventional cystoscopic findings. RESULTS:Twenty - two (69%) of 32 bladder tumors detected during conventional cystoscopy were visualized by virtualcystoscopy. Four (36%) of 11 tumors measured 0.5 cm or less, 15 (83%) of 18 measured 0.5 -3 cm and all (100%) oftumors measured 3 cm or more. With regard to tumor morphology, six (86%) of seven sessile tumors and 16 (64%) of25 which were pedunculated were detected. The procedure was well tol-erated by all patients, and no complicationswere reported. CONCLUSION: Due to its intrinsic weakness, virtual cystoscopy cannot replace itscon-ventional counterpart, though by developing data scan and acquisition techniques and software, and on thebasis of clinical experience, the latter can be used in the future for the diagnosis and follow up ofbladder tumors.