To consider the effects of several years of competitive sports training on children and adolescents with spondylolisthesis, we carried out a retrospective radiologic and clinical study of 86 young athletes with spondylolysis or spondylolisthesis (24 girls and 62 boys between the ages of 6 and 20 years). The mean degree of displacement was 10.1% at the beginning of the observation. The radiologic tests showed an increase in displacement over time in 33 athletes. The average progression of spondylolisthesis in this group was 10.5%. For 36 athletes, spondylolisthesis did not progress during the period of athletic training. In seven athletes, a decrease in the displacement was observed, from 17.9 to 8.9% on average. For 10 athletes, the course of spondylolisthesis could not be determined, because only one lateral radiograph was available. In spite of intensive daily training, the athletes had no symptoms during the entire period of observation, which lasted an average of 4.8 years. In light of our experiments, there is no justification for generally advising children and adolescents with limited spondylolytic spondylolisthesis not to take part in competitive sports.