Abstract Objectives: was to assess the frequency of hypovitaminosis D in patients with ankylosing spondylitis (AS) compared to healthy controls and to evaluate its association with disease activity, structural damage and bone mineral density (BMD). Methods: Serum 25(OH) D in 30 AS male patients was compared to 30 matched healthy controls. AS disease activity was assessed using AS Disease Activity Score and C - reactive protein (ASDAS-CRP). Bath AS Functional Index (BASFI) and Bath AS Metrology Index (BASMI) were used to assess the functional impairment and the spinal mobility respectively. Radiological damage was scored according to modified Stoke AS Spine Score (mSASSS) and BMD was measured in the lumbar spine and femoral neck. Results: The mean serum 25(OH)D levels in AS patients were significantly lower compared to healthy controls (27.73 ± 14.27 vs. 38.46 ± 8.11ng/ml, P Hypovitaminosis D in Ankylosing Spondylitis 2