BACKGROUND: Accumulating evidence documents associations between alterations in hematological parameters, indicative of prothrombotic and proinflammatory states, and risk of metabolic syndrome (MetS). We investigated associations of hematological parameters with MetS and individual criteria of the syndrome among Thai professional and office workers. METHODS: Study subjects were 1,314 patients (531 men and 783 women) who participated in annual health examinations during the period of August through December 2001. MetS was defined using the modified ATP III criteria. Multivariable logistic regression procedures were used to estimate odds ratios (OR) and 95% confidence intervals (95%CI) of MetS risk according to quartiles of each hematological parameter with the lowest quartile specified as the referent group. RESULTS: WBC counts increased with increasing numbers of MetS components in both men and women. Among women, platelet counts, hemoglobin and hematocrit concentrations increased with increasing numbers of MetS components (p<0.05). No similar trends were observed for men. Of the hematological parameters studied, elevated platelet and WBC were statistically significantly associated with MetS among men (OR=1.86, 95% CI: 1.03-3.36; OR=2.26, 95% CI: 1.27-4.02), respectively. Among women, MetS risk increased across successive quartiles of hemoglobin (1.00, 2.63, 3.59 and 4.36; p for trend = 0.002), hematocrit (1.00, 2.35, 3.04 and 5.70; p-for trend <0.001), platelet (1.00, 2.37, 2.83 and 3.11; p-for trend = 0.014) and WBC counts (1.00, 2.97, 4.09 and 5.41; p-for trend < 0.001). CONCLUSIONS: Our data are consistent with an emerging literature demonstrating altered hematological status in patients at high risk of MetS.