OBJECTIVE: This study aims to investigate discriminatory ability of the Systemic Immune-Inflammation Index (SII), Systemic Inflammation Response Index (SIRI), and Neutrophil Percentage-to-Albumin Ratio (NPAR), in differentiating Behçet's Syndrome (BS) organ involvements from mucocutaneous involvement. METHODS: This retrospective cohort study analyzed 436 patients diagnosed with BS from 2018 to 2023. Patients were categorized into three groups based on organ involvement: vascular, only mucocutaneous, and other organ involvement. Receiver Operating Characteristic (ROC) analysis was used to evaluate the discriminatory ability (mucocutaneous vs rest, vascular vs rest). DeLong's test was used to determine statistical differences in discriminatory power between the models. RESULTS: Out of 436, 115 patients had vascular involvement. SII, SIRI, and NPAR were notably elevated in the vascular involvement group ( CONCLUSION: SII, SIRI, and NPAR are promising noninvasive biomarkers for predicting vascular involvement. These indices, derived from routine laboratory tests, could enhance early screening and may improve patient outcomes by enabling timely intervention.