In 20 patients with invasive bladder cancer suitable for radical radiotherapy, a simple conformal planning technique has been compared with conventional beam arrangements in terms of normal tissue sparing. The median treatment volume for the group was reduced from 2275 to 1416 cm3 by the introduction of conformal planning. More specifically, in 13/20 patients (65%) the percentage volume of rectum irradiated to 90% of the isocentric dose was reduced by more than 30%, although the extent of rectal sparing varied greatly between patients. Overall, conformal planning appeared to be less successful at reducing the volume of large and small bowel irradiated to high dose. However, the data suggest that considerable benefit can be expected for those patients most at risk of morbidity by virtue of high bowel volumes included within the treatment length. A randomised trial is now being set up to determine the clinical impact of this planning technique in terms of reduced bowel morbidity.