This was a controlled study to assess the possible role of mechanical trauma in the pathogenesis of some cases of amyotrophic lateral sclerosis (ALS). Questionnaires were sent to 181 patients with ALS who had developed the disease before age 45. Among the 135 respondents 78 (58%) reported having sustained injuries severe enough to have required medical attention prior to the onset of their motor neuron illness. Fifty nine (76%) of the ALS patients reporting an earlier trauma had incurred an injury to the head, neck, shoulder and/or arm. For controls, we used the 85 patients with multiple sclerosis who responded to the questionnaires sent them. The findings of this investigation add further evidence that a former injury may be important in the etiology of some cases of ALS developing early in life.