This report presents a case of a transorbital penetrating brain injury caused by a metal rod. A 47-year-old male injured his left lower eyelid with no witness during working hours. The two days later, he presented with a right hand tremor and abnormal behavior, and was admitted to the hospital. A CT showed a bone fracture of the left orbital roof and a low-density lesion of the left frontal lobe. The initial diagnosis was a cerebral contusion due to a blow-out fracture. However, sagittal MR images on the tenth day in the hospital demonstrated a penetrating tract that was running linearly from the left orbital roof to the left caudate head. Therefore, the final diagnosis was a transorbital penetrating brain injury. This case had no severe complications in spite of the delayed diagnosis. Careful examinations are thus required in order to make a correct diagnosis at the first examination, because a transorbital penetrating brain injury might initially present as a slight wound with no neurological signs.