Objective[|]This study investigated the relation between osteoporosis and vitamin D levels and the disease activity in patients with psoriatic arthritis (PsA).[¤]Materials and Methods[|]In this study, 58 patients with PsA and 58 healthy controls were included. Bone mineral density (BMD) measurements of patients and controls were performed using dual-energy X-ray absorptiometry. Complete blood count, serum 25(OH)D3, parathormone, C-reactive protein (CRP), erythrocyte sedimentation rate (ESR), total calcium, ionized calcium, and phosphorous levels of all participants were measured. Disease activity was evaluated using the Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Disease Activity Index for Reactive Arthritis (DAREA), and the Disease Activity Score 28 (DAS28). The functional status was evaluated using the Health Assessment Questionnaire for the spondyloarthropathies (HAQ-S), and enthesopathy was evaluated using the Maastricht Ankylosing Spondylitis Enthesitis Score (MASES).[¤]Results[|]BMD values of the patients were significantly lower than those of the controls. There was a negative but statistically insignificant relationship between the lateral lumbar BMD values of the patients and clinical activity signs. Vitamin D levels of the patients were significantly lower than those of the controls. Although there was no correlation between vitamin D levels and ESR and CRP levels, a negative but statistically insignificant relation was found between vitamin D levels and BASDAI, DAREA, and DAS28. The level of CRP, BASDAI, MASES, DAREA, HAQ-S, and DAS28 scores were higher in the patients with osteoporosis; however, none of the differences were statistically significant.[¤]Conclusion[|]In this study, the incidence of osteoporosis was higher and vitamin D levels were lower in patients than in controls.[¤]