To assess the efficiency of systemic immune-inflammation index (SII) in determining activation of Behcet disease.This retrospective cohort study was conducted among patients with Behcet Disease who admitted to the outpatient clinic of Department of Dermatology and Veneorology, Ufuk University Hospital between January, 1, 2010 and December, 31, 2019. Patients were divided into two groups based on their disease status upon admission: 1)Active Behcet Disease (n=103) and 2)Inactive Bahcet Disease (n=63). Clinical characteristics, demographic features, type of medications, complete blood count parameters, erytrocyte sedimentation rate (ESR), C-reactive protein (CRP), ferritin and SII were compared between the groups. Furthermore, a receiver operating characteristic (ROC) curve analysis was performed in order to assess the performance of SII in determining the patients' status of the disease upon admission to hospital.Higher levels of white blood cell, platelet, neutrophile, red cell distribution width, ESR, CRP, ferritin and SII were observed in the active disease group (<0.001). The cut-off value of 552.12 103 /mm3 was found with 81% sensitivity and 82% specificity.SII may be used as an additional indicator for the assessment of Behcet disease status and physicians should be cautious in SII levels of >552.12 (103/mm3) at the initial evaluation of the patients.