Patients with lumbar spondylolysis may have poor lumbo-pelvic function and improving lumbar segmental stability may take time. It is assumed that the stronger the lordosis, the poorer the lumbo-pelvic function; however, to our knowledge, evidence of this relationship is lacking. To clarify the relationship between lumbosacral alignment and lumbo-pelvic function in lumbar spondylolysis, we assessed lumbar lordosis and sacral slope in the standing lateral view on plain X-rays and Sahrmann Core Stability Test (SCST) results in 66 adolescents with lumbar spondylolysis with bone marrow edema. Based on SCST results, the patients were divided into those with level 1 or 2 core stability (low group) and those with level 3 or higher core stability (high group). No significant difference was found in lumbosacral alignment between the two groups. In adult patients with spondylolisthesis, the lumbar lordosis angle and sacral slope increases to maintain the center of gravity, but no such increase in compensation was evident in our patients who were young and without slip. These findings suggest that lumbo-pelvic function does not affect lumbosacral alignment in adolescents with spondylolysis. It should be noted that using the SCST alone to evaluate motor control may not be precise enough to determine the relationship between lumbosacral alignment and lumbo-pelvic function because the SCST may not have high enough sensitivity to assess trunk extensor muscles.