From a population of 1,503 schoolchildren, 38 15-year-old children suffering from low-back pain and 38 asymptomatic controls were selected for testing of spinal mobility and trunk muscle strength. The asymptomatic controls were matched by age, sex, and school class. In the group with recurrent or continual low-back pain (17 boys and 21 girls), the boys were over 4 cm taller than those in the control group. In both sexes sagittal mobility was decreased in lumbar extension and straight leg raising, and increased in lumbar flexion. Endurance strength in the abdominal and back muscles was decreased compared to the control pupils, who reported no back pain at all in the questionnaire collected 1 year before the testing procedure. The pupils reporting sciatica (n = 7) at some time, in addition to recurrent low-back pain, had decreased lumbar flexion and side bending compared to those with recurrent low-back pain (n = 31) without sciatica. The results of the study indicated that in this growing-age population there was a subgroup with recurrent low-back pain having a different spinal mobility pattern as well as decreased trunk muscle strength.