The spinal cords of 19 percent of patients dying with cystic fibrosis after 5 years of age showed posterior column degeneration. The risk did not appear to increase with advancing age. None of these patients had findings of pernicious anemia or spinocerebellar degeneration. The lesions had been undetected clinically. It is possible that nutritional, toxic, or hereditary factors may play a role in producing this lesion.