Patients with high thoracic or cervical spinal cord injuries normally have a detrusor contraction during cystometry. Thirteen patients with detrusor areflexia and a high spinal cord lesion underwent neurophysiological evaluation with electromyography of the pelvic floor muscles, lumbosacral-evoked potential to tibial nerve stimulation, the bulbocavernosus reflex and water cystometry. Two groups of patients were identified. Of those patients with initial detrusor areflexia evidence was found for a subclinical second lesion involving the lumbosacral arc, which accounted for the acontractile bladder. In the remaining patients of this group, who had an intact sacral reflux arc, a detrusor contraction developed after a mean of 16.6 months from the date of injury. The second group of patients exhibited initial detrusor hyperreflexia that subsequently converted to areflexia. A reason was found for the alteration in bladder behavior in each case. The possible reasons for differential recovery of the somatic and autonomic nervous systems are discussed together with a rationale for the second subclinical spinal cord lesion. The most predictive neurophysiological test was electromyography of the pelvic floor.