Patients with upper and lower motor neuron spinal cord injuries were observed to determine whether cystography immediately before excretory urography induced iatrogenic dilatation of the upper urinary tract that was indistinguishable from true pathological dilatation. Evidence is given that such dilatation occurs. This iatrogenic dilatation is not seen in patients with normally innervated urinary tracts and appears to be caused by exaggerated bladder reflexes in patients with upper motor neuron lesions. Bladder spasms precipitated by cystographic contrast material also may create vesicoureteral obstruction and lead to dilatation of the upper urinary tract. Consequently, it is suggested that cystography should not immediately precede excretory urography. When such a sequence is necessary, room or body temperature contrast medium should be used for the cystogram, the bladder should be emptied before the excretory urogram is started and a 1-hour interval should be allowed between the 2 procedures. The findings also suggest that any factors that induce repeated or continuing bladder spasms may contribute to progressive dilatation of the upper urinary tract.