Herniated lumbar disc or definite sciatica was diagnosed in 16 of 195 men and women who had reported a history of low-back pain in a health survey. Measurements related to the size and shape of the lumbar spinal canal were subsequently made from the survey radiographs and compared between various types of back syndromes. Age, body height, body mass index, occupation, and parity of women were controlled as potential confounders using analysis of covariance. Several dimensions of lumbar vertebral canals appeared more shallow in the subjects who had herniated disc or definite sciatica than in the other ones. In particular, the interarticular distance of the first sacral vertebra was found to be narrowed in the presence of sciatica, the difference of the adjusted distances to the other back pain category being in men 30.5 mm versus 35.1 mm (P = 0.02) and in women 23.8 mm versus 30.3 mm (P = 0.002), respectively.