Objective: Behçet's Disease (BD) is a polygenic and chronic autoinflammatory multisystemic vasculitis disease characterised by mucocutaneous, musculoskeletal, neurological, gastrointestinal and ophthalmologic lesions. There has been no specific test or serum marker to measure and determine the diagnosis and severity of BD. Purpose: The study aimed to investigate the diagnostic performance of haematological parameters as MLR (monocyte to lymphocyte ratio), NLR (neutrophil to lymphocyte ratio), PLR (platelet to lymphocyte ratio), MPV (mean platelet volume), MPVPR (mean platelet volume to platelet ratio), LMR (lymphocyte to monocyte ratio), LPM (lymphocyte and platelet multiplication), WLP (lymphocyte and leukocyte multiplication), RDW (red blood cell distribution width) and PCT (plateletcrit) in BD and compare these with disease activity and clinical findings. Methods: A total of 266 participants (49 healthy control and 217 BD patients) were recruited from the rheumatology department in a single-centre as a case-control study. The laboratory data were obtained from the electronic registration database. BD Activity scores (BDCAF/Behcet's Disease Current Activity Form) were calculated. Laboratory findings of BD patients and healthy controls were compared and evaluated. Results: RDW, Platelet, PCT, NLR and PLR values were significantly higher in patient group than in the healthy controls. However, haemoglobin, MPVPR and LMR were significantly lower in the patient group which compared with the healthy controls. LPM in BD with genital ulcers, WLP in BD with genital ulcers and arthritis, MPR in BD with uveitis, RDW in BD with thrombosis and neuro-Behçet's disease (NBD), PLR in NBD were observed to be higher. However, LMR in NBD and MPV in BD with thrombosis were lower than those without. There was a positive correlation between BDCAF score and RDW, and NLR. Conclusion: Haemoglobin, RDW, Platelet, PCT, NLR, LMR, PLR and MPVPR were statistically significant predictors for BD. RDW, PCT and NLR are the most valuable predictors for BD.