Periodontal diseases are frequently associated with cardiovascular diseases (CVD). On the other hand, occurrence of CVD has also been related with increased blood viscosity. This study was planned to investigate four main hemorheological parameters contributing to blood viscosity -hematocrit, erythrocyte deformability, erythrocyte aggregation and plasma viscosity - and also some biochemical parameters (hs-CRP, fibrinogen, globulin etc.) in patients with periodontal disease. We hypothesized that poor periodontal health would be associated with deterioration of hemorheological properties. According to periodontal health status, subjects were divided into three groups as control (healthy), with plaque induced gingivitis and with chronic periodontitis. All groups included 15 males who had not received periodontal therapy in the last six months before the study, were non-smokers, had no systemic diseases and were not on any medication. Erythrocyte deformability and erythrocyte aggregation were measured with laser-assisted optical rotational cell analyzer (LORCA). Plasma viscosity was measured by a cone-plate viscometer. Data were analyzed with Kruskal-Wallis, Mann-Whitney U Test and Spearman Correlation Coefficient. Plasma viscosity (1.36 +/- 0.01 mPa.s in the control group and 1.43 +/- 0.02 mPa.s in the chronic periodontitis group, P < 0.01), erythrocyte aggregation tendency (aggregation index, amplitude and t(1/2) were 58.82 +/- 1.78%, 20.22 +/- 0.40 au, 2.80 +/- 0.25 s respectively in the control group, and 67.05 +/- 1.47%, 22.19 +/- 0.50 au, 1.84 +/- 0.15 s in the chronic periodontitis group, P < 0.01), hs-CRP, fibrinogen and globulin levels were significantly higher, whereas HDL level was significantly lower in the chronic periodontitis group (P < 0.05) compared to the control group. All of these conditions may contribute to cardiovascular morbidity and mortality observed in people with periodontal disease, via increasing blood viscosity.