A 9-year-old girl with rigidospastic quadriplegia as post-traumatic sequela was reported. The distribution of lesions observed on a MRI implied diffuse axonal injury; involvement of the substantia nigra was also detected. L-Dopa administration was remarkably effective for relief of the rigidity. As a result, she became able to walk on her knees and communicate by writing letters. L-Dopa administration should be considered for patients who show rigidity as sequela of diffuse axonal injury with involvement of the substantia nigra.