Cross-sectional study.To compare the prevalence of lumbar spondylolysis and spina bifida occulta (SBO) in pediatric and adult populations.The prevalence of spondylolysis reported from radiograph-based studies in children had been questioned in computed tomography (CT)-based studies in adults; however, a recent CT-based study in pediatric patients has confirmed the previously reported data in pediatric populations. SBO, which has been associated with spondylolysis, has demonstrated a decreasing prevalence with increasing age during childhood and adolescence. No studies have compared the prevalence of spondylolysis and SBO in pediatric and adult patients using CT as a screening method.We studied 228 pediatric patients (4-15 y old) and 235 adults (30-45 y old) who underwent abdominal and pelvic CT scans for reasons not related to the spine. The entire lumbosacral spine was evaluated to detect the presence of spondylolysis and SBO. We compared the prevalence of spondylolysis and SBO in pediatric patients and adults.The prevalence of spondylolysis in pediatric patients was 3.5% (1.1%-5.9%), and in adults, it was 3.8% (1.7%-6.8%), P=1. The prevalence of SBO in pediatric subjects was 41.2% (34.8%-59.2%) and dropped to 7.7% (4.3%-11.5%) in adults, P<0.01. The male prevalence of SBO in pediatric patients was 51.4%, whereas it was 32.2% in females (P<0.01); this sex difference was not significant in the adult population (P=0.8).The prevalence of lumbar spondylolysis remained constant from pediatric age through adulthood. The prevalence of SBO decreased from 41.2% in children to 7.7% in adults; this finding suggests that closure of the vertebral arch may not be completed in early childhood in a large percentage of subjects.