OBJECTIVE:To investigate the characteristics of epidemiological distribution of the ossification of the ligamentum flavum (OLF) in the thoracic spine including the incidence, segmental distribution, and shape. METHODS:Chest spiral computed tomography scans of 993 cases (male 506, female 487, mean age 60 years, range 5-102 years) who presented due to chest symptoms were analyzed with axial slices combined with sagittal slices. The conditions of OLF in the thoracic spine, including segments, thickness, location, and dural sac compression, were recorded. Prevalence was standardized according to the "Age Structure of Population in Beijing 2008". RESULTS:Among the population investigated, the standardized prevalence rate was 63.9 %. The standardized prevalence rate for males (68.5 %) was higher than that for females (59.0 %). The highest prevalence rate of OLF was in the 50-59 years age group (79.2 %); however, high density originated it can be found in individuals aged 10-19 years. The comparison of different thoracic segments showed that T10-11 (44.0 %) and T11-12 (41.6 %) had the highest prevalence rates. CONCLUSION:The prevalence of ossification of the ligamentum flavum was highest in the 50-59 years group, but also occurred in early years. OLF occurs more frequently in the lower than in the upper and middle thoracic regions and its prevalence increases with aging.