The study of the lumbar canal sizes in Chinese has not been reported before. Thirty adult patients, aged 20 to 40 years, who sustained thoracolumbar or lumbar fracture-dislocation and needed further computed tomographic (CT) scanning were included in this study. There was no significant back pain or sciatica on these patients before. Measurements of the med-sagittal anteroposterior (A-P) and interpedicular (I-P) diameters of the spinal canals L1 to L5 were requested at the same time during CT scanning. The results show that the lowest normal limits of the A-P and I-P diameters of the lumbar canals in Chinese are 11 mm and 19 mm respectively. The I-P diameters increase progressively from the first to the fifth vertebrae. The A-P diameters, however, are more variable and shortest at L2, L3 and L4 vertebrae.