In a prospective study the authors correlated the degree of hematuria and of blunt abdominal trauma with the results of emergency excretory urography. Urograms were obtained for 37 patients who presented with blunt abdominal trauma, no gross hematuria and at least five erythrocytes per high-power field (hpf) on microscopic urinalysis. Microscopic hematuria was defined as an erythrocyte count of more than 5 and fewer than 50 per hpf. Major trauma was defined as shock (systolic blood pressure of less than 90 mm Hg), fracture of the lumbar spine, the pelvis or the lower ribs, ecchymosis in the flank or acute abdominal injury. Contusions and small subcapsular hematomas were defined as nonsignificant renal injuries; all other renal injuries were defined as significant. Of 17 patients with minor blunt abdominal trauma 14 had fewer than 50 erythrocytes per hpf; none of these had a significant renal injury, whereas 1 of the 3 with more than 50 erythrocytes per hpf did have a significant injury. Of 20 patients with major trauma 5 had a significant renal injury. The authors conclude that microscopic hematuria associated with blunt abdominal trauma but without shock or major nongenitourinary injury does not warrant routine excretory urography.