Osteoporosis is a metabolic bone disease that is also accompanied by reduced bone density. It most often occurs in the elderly population, frequently in postmenopausal women, and as a complication of other bone or extra-osseous diseases. Osteoporosis often causes osteoporotic fractures that occur even with mild or minor trauma. Ankylosing spondylitis (AS) is a chronic inflammatory disease with a tendency to progression. It affects the axial skeleton, especially the vertebral and sacroiliac joints. In the general population, its prevalence is about 0.2%, and it occurs more often in younger men. It shows a strong association with the HLA-B27 antigen. Chronic inflammation associated with numerous inflammatory cytokines lead to bone microarchitecture damage. This reduces bone mineral density and increases the risk of osteoporosis, the latter being one of the complications of AS. If osteoporosis occurs in patients with AS, it further increases the risk of fractures. However, unlike postmenopausal osteoporotic fractures, these fractures more often affect the cervical spine with more pronounced symptoms, and can also lead to neurological dysfunction. The most important risk factors favoring the development of osteoporosis in AS patients are chronic inflammation (especially important pro-inflammatory cytokines TNF-alpha, IL-1, and IL-6) which stimulate bone breakdown, and reduced physical activity due to vertebral ankylosis. Fractures are the cause of increased mortality compared to the healthy population, and are treated with immobilization or surgery. The diagnosis of fractures is difficult because they are hard to identify on X-ray, due to the abundance of osteophytes. Hence, CT is the method of choice.