OBJECTIVE The purpose of this study was to determine whether routine bowel preparation with laxatives and dietary restrictions (liquid supper and fasting after midnight) are necessary for satisfactory visualization of the urinary system during excretory urography in outpatients. METHODS Two hundred and four consecutive patients who had excretory urography were randomly placed in one of four groups before the examination. Eleven patients were excluded from the study for various reasons. The remaining 193 were divided into four groups. Groups 1 (50 patients) and 2 (45 patients) had bowel cleansing; groups 3 (49 patients) and 4 (49 patients) did not. Groups 1 and 3 were allowed to eat; groups 2 and 4 were given a liquid supper and fasted beginning at midnight the night before the examination. Standard radiographs and tomograms were obtained. Upon completion of excretory urography, the radiographs were reviewed and graded by one radiologist, who did not know to which group each patient belonged. A detailed, anatomically based grading system was developed and used to grade the radiographs. The radiographs of the kidney were divided into upper, middle, and lower margins; images of the calices were divided into upper, middle, and lower segments; images of the renal pelvis were divided into central and medial margins; images of the ureter were divided into upper abdominal, lower abdominal, upper pelvic, and lower pelvic categories; and images of the bladder were divided into full and empty categories. A score of 1 was given to each section visualized. The right and left sides of the urinary system were scored separately but added together for statistical analyses; therefore, the highest total score possible was 28. RESULTS In the ability to visualize the anatomic structures on excretory urograms, there was no statistically significant difference (p = .06) between images of patients who were allowed to eat (groups 1 and 3, 99 patients, mean score = 27.49 +/- 0.92) and images of patients who were given a liquid supper and then fasted from midnight the night before excretory urography was performed (groups 2 and 4, 94 patients, mean score = 27.16 +/- 1.45). Moreover, there was no statistically significant difference (p = .16) between those patients given laxatives before the examination (groups 1 and 2, 95 patients, mean score = 27.45 +/- 0.93) and those not given laxatives (groups 3 and 4, 98 patients, mean score = 27.20 +/- 1.43). CONCLUSIONS Our results show that bowel preparation with laxatives and dietary restrictions do not improve visualization of the urinary tract on excretory urograms obtained in outpatients. We conclude that such preparation in this group of patients was unnecessary and that it need not be performed routinely.