Trauma to the back from the force of chronic stress is thought to be an etiologic factor in isthmic spondylolisthesis (SLL). The relationship of first degree spondylolisthesis to low back pain (LBP) is controversial. We compare the prevalence of SLL in helicopter pilots who are subject to strong vibrational forces, with other airforce personnel. Helicopter pilots had more than a four times higher prevalence of SLL (4.5%) than did cadets (1.0%) and transport pilots (0.9%). Low back pain was more frequent in pilots with SLL than in those without this lesion but in no case was the pain disabling or the defect progressive. We conclude that SLL may be induced by vibrational forces and although SLL is associated with LBP, the pain was little clinical significance.