Six children who complained of pain and stiffness in the back had been treated with lumbar punctures between six and ten years before they came under observation. They were found to have intrathecal epidermoid tumours in the lumbar region which are presumed to have arisen from implanted skin fragments. The main evidence for this assumption is that since 1956 sixteen patients with lumbar epidermoid tumours in patients who had had previous lumbar punctures have been reported, in contrast to the five patients with lumbar epidermoid tumours recorded before that date. This suggests that there is an additional etiological factor.