Despite a lack of hard evidence, many radiologists continue to support the use of fluid restriction before urography. Based on increasing the urinary contrast medium concentration, this has been shown to be a poor index for renal opacification. The usual overnight restriction produces no significant change in urine osmolality or opacification. Effective fluid restriction may produce a just detectable increase in pyelographic density but the nephrogram in unaffected, even by active hydration. Fluid restriction may occasionally result in inadvertent dehydration with serious or fatal reactions. Since it is ineffectual in improving the urogram and potentially hazardous, it should be abandoned.