Eighteen patients with probable blunt injury of the kidneys were referred for ultrasonography (US). Eleven of them presenting abnormal US findings were retrospectively reviewed for their renal injuries. US classification of the renal parenchymal injury was done according to computed tomographic staging. Four were of minor laceration and six were of major injury. The last one with preexisting hydronephrosis was not staged because there was no ultrasonically demonstrable focal parenchymal lesion. The US findings of the injured kidneys included focal change of parenchymal echopattern, contour change, subcapsular or perirenal fluid accumulation, increased renal length and intraabdominal fluid collection associated with abdominal visceral organ injury. Major vascular injury of the kidney may be further assessed by color Doppler US. It is reliable to evaluate the extent of renal injury in detail by US, that could be a favorable screening examination and an effective follow-up imaging tool.