Patients with ankylosing spondylitis are susceptible to spinal fractures. In many cases there is no history of associated trauma or only minor trauma. The instability of such fractures and complicating neurologic sequelae are well documented. We describe an unusual complication of ankylosing spondylitis, hemothorax secondary to spinal fracture, that to our knowledge has not been previously reported. Further, we reemphasize that the instability of such fractures may lead to significant paravertebral soft tissue and vascular injuries.