OBJECTIVE: To determine RDW and MPV levels in Ankylosing Spondylitis (AS) and to investigate their relations with disease activity. MATERIALS AND METHODS: 133 patients with AS (male: 80, female: 53) and age-sex matched 133 controls (male: 79, female: 54) were enrolled. Demographic data, disease activity scores, Complete Blood Count (CBC), Erythrocyte Sedimentation Rate (ESR) and C-Reactive Protein (CRP) levels were recorded. RESULTS: The mean ages of patients and controls were 41.9 +/- 11.2 and 39.7 +/- 14.2 years respectively (p = 0.16). RDW (14.5 +/- 1.6% and 13.2 +/- 0.8%, p4) and those with inactive AS (BASDI < 4) patients (14.84 +/- 1.79fl, 14.24 +/- 1.37fl, p = 0.035 respectively). RDW was positively correlated with BASDAI (r = 0.33, P < 0.0001), ESR (r = 0.45, P < 0.0001) and CRP (r = 0.42, P < 0.0001) and PLT levels (r = 0.24, P = 0.004). While MPV was not correlated with BASDAI, it was negatively correlated with ESR (r = -0.19, P = 0.03), CPR (r = -0.26, P = 0.004) and PLT levels (r = -0.39, P = < 0.0001). CONCLUSIONS: RDW and MPV were significantly higher in the patients with AS than in the controls. While RDW was correlated with BASDAI and APRs, MPV was only correlated with APRs.