A 77-year old woman presented a Brown-Séquard syndrome of sudden onset at level C4, and a few days later a tetraplegia. Postmortem findings demonstrated, at C3-C4, a left spinal cord infarct accounting for the Brown-Séquard syndrome, and a second C5-C6 bilateral infarct responsible for the tetraplegia. Alternating distribution of sulcal arteries explains the limitation of the first lesion to one half of the spinal cord.