We studied prospectively 359 consecutive patients with blunt (306) or penetrating (53) renal trauma to refine the indications for radiographic evaluation. Various factors, including the degree of hematuria, presence of shock and associated injuries easily assessable at the time of initial evaluation, were correlated with the severity of renal injury to determine whether any combination of parameters will separate patients with renal contusions from those with significant renal injuries (minor and major lacerations, and vascular injuries). We identified 3 groups: group 1-85 patients with gross hematuria or microscopic hematuria and shock after blunt trauma (including all 23 with significant renal injuries), group 2-221 patients with microscopic hematuria but no shock after blunt trauma (all with renal contusions) and group 3-53 patients with penetrating trauma. No combination of parameters was able to predict a severe injury in group 3. Our data support radiographic evaluation in groups 1 and 3. However, because all patients in group 2 had renal contusions and experienced no complications from nonoperative management we believe that excretory urography, which is time-consuming and costly, can be avoided in patients with microscopic hematuria but no shock after blunt renal trauma.