Increased coagulation factor levels have been demonstrated to be a risk factor for venous thromboembolism in patients of Caucasian origin. Coagulation factors, hereditary thrombophilia, and ABO blood group were evaluated for venous thrombosis risk in a heterogeneous Brazilian population consisting of 122 women and 53 men, with a median age of 36 years (range 13-63), matched to a control group by age, sex, and ethnicity. Increased levels of factor VIII (odds ratio [OR], 3.1; 95% confidence interval [CI], 1.6-6.0), von Willebrand factor (OR, 2.8; 95% CI, 1.4-5.4), non-O blood group (OR, 2.1; 95% CI, 1.3-3.4), and thrombophilia (OR, 3.4; 95% CI, 1.6-7.1) emerged as independent risk factors for venous thromboembolism. The interaction of high levels of factor IX and factor XI with other independent variables increased the potential for thrombosis synergistically. Therefore, the ability of identifying underlying thrombophilia risk factors in our population was enhanced by the inclusion of these factors in the prothrombotic laboratory workup.