Parachuting, be it static line or skydiving, places enormous stresses on the human spine. It is, therefore, important to determine the prevalence and severity of degenerative changes in the lumbar spine of subjects who practice this sport activity. Seventy four parachuting instructors, mean age 33 years and with an average of 410 static line and skydiving jumps, were included in the study. Past radiographs were examined and compared to current anterolateral and lateral views of the lumbar spine, in order to determine the prevalence of degenerative changes and document possible progression. Doubtful radiographic changes in the lumbar spine were identified in 47.4 percent of the parachuting instructors, mild degeneration in 9.6 percent, moderate degenerative disease in 10.9 percent and severe radiographic changes in 5.5 percent. Schmorll nodes were found in 8.1 percent of the subjects. Traction spurs--osteophytes were identified in 6.8 percent. The degenerative changes correlated with age and the number of jumps. Spondylolysis of L5-S1 and L3-L4 segments were observed in 12.2 and 1.4 percent respectively. Progressive spondylolisthesis was found in 2 subjects. No correlation was found between the severity of radiographic changes and either the prevalence and the severity of low back pain. The present findings provide a rational for considering repeated sheer stress as an etiology of degenerative changes in the spinal cord, and as a possible contributing factor to the pathogenesis of spondylolysis. Further study has to be done comparing parachuting instructors to a non-parachuting group, or equivalent physically active individuals, in order to assess the effect of sport-background on the development of degenerative changes.