Radiographs were obtained of the lumbosacral spines of 143 patients that had never walked. The frequency of spondylolysis and spondylolisthesis was determined, as well as that of other spinal abnormalities. The average age of the patients was 27 years, with a range of 11 to 93 years. The underlying diagnoses responsible for the nonambulatory status varied, but cerebral palsy predominated. No case of spondylolysis or spondylolisthesis was detected, and when compared to the 5.8% incidence in the general population, this finding is significant at the P less than 0.001 level. The incidences of spinal bifida (8.4%) and of transitional vertebrae (10.9%) are similar to those found in the general population. Scoliosis was found in 49% and vertebral body height was increased in 32.9%. Degenerative changes occurred in only 2.8%. These results support the theory that spondylolysis and isthmic spondylolisthesis represent a fatigue fracture resulting from activities associated with ambulation.