Whether or not bowel preparation should be used before intravenous urography (IVU) remains a controversial issue. Despite strongly held views on both sides there is little scientific evidence to support either viewpoint. We have conducted a prospective randomized study designed to test the hypothesis that adequate bowel preparation before IVU facilitates better quality studies requiring fewer films and consequently less time and a lower radiation exposure. Data on 188 patients were analysed; 90 patients received bowel preparation and 98 received no bowel preparation. There was no difference between the groups in terms of the number of films taken, the duration of the procedure, the visibility of the renal tracts or the overall quality of the studies. The prepared group did have significantly less faecal residue than the unprepared group. However, the renal tract visibility was no greater, as the combination of gas and haustral folds seen after bowel preparation obscured fine detail of the urinary tract as effectively as faecal residue. The hypothesis that adequate bowel preparation before IVU facilitates better quality studies must therefore be rejected.