In a roentgenographic analysis of the lumbar spine of 100 young female gymnasts engaged in high-level competition, the incidence of pars interarticular defects was 11 per cent; 6 per cent had spondylolisthesis. This is 4 times higher than their non-athletic female peers. It appears that the female athlete may have the same incidence of pars interarticularis defects as the male performing similar activities. Pars defects developing in association with athletic activities may be distinct from those developing in early childhood. A negative lumbosacral roentgenographic series does not completely rule out a developing pars defect. Bone scintography offers an additional tool for evaluating early stress reaction in the pars, and suggests that if the athlete restricts vigorous activity, some will heal without progressing to roentgenographically detectable defects. Low back pain in the young gymnast should be a warning sign. Close scrutiny of pars interarticularis in these young athletes will reveal a high incidence of developing defects.