Bladder function was evaluated urodynamically in 17 patients operated on 2 to 3 years previously for the cauda equina syndrome caused by a prolapsed lumbar intervertebral disk. Of the patients 10 (59 per cent) reported the bladder function to be normal, while the other 7 had symptoms of obstruction or incontinence. Urodynamic findings were normal in 4 patients (24 per cent). In 3 patients (18 per cent) no detrusor contraction could be demonstrated in the pressure-flow electromyography study. Two patients (12 per cent) used the detrusor and straining during voiding. Cystometry showed an unstable detrusor in 3 patients (18 per cent). The remaining 5 patients (29 per cent) had either an increased bladder capacity or a decreased maximum flow rate. Neurological findings were normal in 2 patients (12 per cent). All of the patients with a decentralized detrusor had defective perianal sensation but detrusor contraction could be demonstrated in 3 who also had sensory impairment in the perianal region. Bladder function can be disturbed seriously in cauda equina patients without symptoms and, thus, all patients with the cauda equina syndrome should be tested urodynamically. An emergency operation seems to be capable of reducing late disturbances in bladder function. Regeneration of the autonomous nerves supplying the bladder and genitals may require an interval of several months to years.