Introduction: Brucellosis is an inflammatory disease capable of infecting any organ and system in the body. Mean platelet volume (MPV) serves one of the most commonly used surrogate markers of platelet function. It has been shown that MPV reveals the existence of disease activity in a great number of inflammatory diseases. Red blood cell distribution (RDW) serves as a measure of the heterogeneity of the sizes of the circulating red blood cells. Its predictive value for inflammatory and infectious diseases has been proved. The aim of this study was to investigate whether MPV and RDW could have any role in the diagnosis of cases with osteoarticular involvement or relapsed brucellosis. Materials and Methods: The present study was carried out by prospectively examining the inflammatory markers detected in adult patients with brucellosis between 2008 and 2014. Their follow-ups in the year after treatment were also examined. Results: The study included two hundred and fifty patients in the acute brucellosis group and 101 patients in the control group, adding up to a total of 351 subjects. In the relapsed brucellosis group the mean MPV and RDW values were 7.52 ± 1.18 fL and 16.24 ± 1.91%, respectively, while they were 7.77 ± 1.52 fL and 15.95 ± 1.55%, respectively in the control group (p< 0.001). No significant difference was found in the osteoarticular involvement group when compared to the controls. Conclusion: The study revealed that MPV, RDW and blood leukocyte count values in patients with relapsed brucellosis and with os-teoarticular involvement were within normal limits and comparable with the control group. In cases of brucellosis with osteoarticular involvement, the most valuable inflammatory marker is still the CRP value. ÖZET