Isolated injury of the spinal accessory nerve is a well-recognized complication of surgeries involving the posterior triangle of the neck. The procedures most commonly implicated are lymph node biopsy and carotid endarterectomy. We present a patient with isolated injury to the spinal accessory nerve, localized proximal to the innervation of the sternocleidomastoid muscle, which was noted following suboccipital decompression for an Arnold-Chiari malformation. To our knowledge, this association has not been previously reported.