Objective. The aim of this study was to analyze bone mineral density (BMD) in patients with seronegative spondylarthropathy, to determine the frequency of osteoporosis, to investigate the relationship between BMD and clinical, laboratory, and radiological variables in patients with seronegative spondyloartropathy, to define the relationship between bone growth (syndesmophytes) and bone loss, and to determine the frequency of vertebral fractures. ----- Methods. 237 patients with seronegative spondyloartropathy (157 women, 80 men) and 100 healthy controls were recruited to the study. Lumbar spine, hip and forearm BMD were measured by dual energy X-ray absorptiometry. Radiographs of the lumbar spine were used to analyze syndesmophytes and vertebral fractures. ----- Results. Compared with age-matched controls, patients with seronegative spondyloartropathy had a significantly lower BMD in the lumbar spine (1,217±0,148 g/cm2 vrs 1,049±0,216 g/cm2) and in the total hip (1,086±0,168 g/cm2 vrs 0,968±0,174 g/cm2), (p<0,001). Osteoporosis was observed in 57 (24,1%) patients. Presence of syndesmophytes and vertebral fractures significantly correlated with BMD. Vertebral fracture was observed in 99 (41,8%) patients. ----- Conclusion. Patients with seronegative spondyloartropathy had lower BMD in comparison with healthy controls. The demineralization was related to the disease duration, low bone mass index, smoking and the number of years since menopause. Bone mass loss in seronegative spondyloartropathy is better evaluated at the femur because syndesmophytes are common finding in this group of patients.