The present study was designed to investigate the interaction between platelet indices, inflammatory markers and disease activity in rheumatoid arthritis (RA) subjects. The effects of anti-TNF-alpha therapy and conventional treatment on platelet indices were also compared. We studied 97 patients with RA (19 men, 78 women: mean age 51 years) and 33 age and sex-matched healthy subjects as a control group. All RA patients were administered conventional therapy. After 3 months of therapy, 35 subjects who had high disease activity score (DAS28 > 5.1) were grouped as non-responders and were administered infliximab as a TNF-alpha blocker at the standard intravenous dose. Responders to the conventional therapy and non-responders were also compared. At baseline white blood cell (WBC), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), platelet count and mean platelet volume (MPV) were significantly higher in patients with RA. Mean platelet volume was positively correlated with DAS28 score (r = 0.27; p = 0.007). These markers of inflammation and platelet indices were substantially decreased after therapy. The reductions were similar in responders to conventional therapy and non-responders (TNF alpha group). In conclusion, we found that MPV was correlated with inflammatory markers and disease activity in patients with RA. Both anti-TNF-alpha and conventional therapy decreases markers of inflammation and platelet indices. MPV can reflect both disease activity and response to treatment.