Vertebral deformation in spinal osteoporosis results in spinal and thoracic deformation, causing pain, disability and an overall decrease in quality of life. We sought to determine whether thoracic spinal deformation may lead to impaired pulmonary function. We studied expiratory relaxed vital capacity (VC) and forced expiratory volume in 1 s (FEV1) in 34 patients with spinal osteoporotic fractures and 51 patients with chronic low back pain (CLBP) due to reasons other than osteoporosis. Measurements of pulmonary function tests were calculated as a percentage of the normal range adjusting for age, sex, and height using the equations for normal values of the EKGS (Europäische Gesellschaft für Kohle und Stahl). Severity of osteoporosis was determined by calculation of the spine deformity index (SDI-total and SDI-anterior) on lateral radiographs of the spine and clinical measures of body stature (height reduction, distance from lowest ribs to iliac crest and distance from the occiput to the wall). Patients with osteoporosis had a lower vital capacity (%VC of the reference value) than patients with CLBP. The differences were more prominent (p < 0.05) when the previous body height, at age 25 years, was used as reference for calculation of VC (mean +/- SD: 93.6% +/- 15.3% in patients with osteoporosis v 105.6% +/- 15.1% in patients with CLBP). FEV1 was significantly (p < 0.05) lower in patients with osteoporosis when previous body height was considered, in comparison with patients with CLBP (mean +/- SD: 85.0% +/- 14.2% in patients with osteoporosis v 92.4% +/- 13.6% in patients with CLBP). In patients with osteoporosis VC (standardized on previous body height) was significantly negatively correlated with SDI-anterior (r = -0.4, p < 0.03). Furthermore, VC standardized on previous body height showed a weak but significant negative correlation with some clinical measures of osteoporosis (height reduction vs %VC: r = -0.34, p < 0.05; distance from the lowest ribs to iliac crest vs %VC: r = 0.35, p < 0.04). In conclusion, we found that pulmonary function is significantly diminished in patients with spinal osteoporotic fractures as compared with CLBP patients without evidence of manifest osteoporosis. Reduction of pulmonary function is correlated significantly with clinical and radiological measures of severity of spinal deformation due to osteoporotic fractures.