Ankylosing spondylitis (AS) is a chronic inflammatory disease of the axial skeleton.Interleukin-37 (IL-37) is a member of IL-1 family cytokines, that downregulate expression of pro-inflammatory cytokines in chronic inflammatory diseases. The aim of the work is to investigate role of IL-37 in AS disease activity and osteoporosis. Twenty-five patients with AS and 25 controls were enrolled into this study. They were subjected to full clinical examination including assessment of disease activity according to the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI). Serum IL-37 levels and IL-37 mRNA relative concentration were measured by enzyme-linked immunosorbent assay (ELISA) dna quantitative reverse transcriptase- polymerase chain reaction (RT–PCR) respectively. Bone mineral density (BMD) was determined using dual energy X-ray absorptiometry (DEXA). Spine radiographs were scored using the modified Stoke Ankylosing Spondylitis Spine Score (mSASSS). Mean serum IL-37 level was significantly higher in AS patients compared with the controls (P