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Hematocrit above the normal range for the population, such as in primary or secondary erythrocytosis, predisposes to both arterial and venous thrombosis. However, little is known about the association between hematocrit and risk of venous thromboembolism in a general population. Design and Methods Hematocrit and related hematologic variables such as hemoglobin, red blood cell count, mean corpuscular volume, and baseline characteristics were measured in 26,108 subjects, who participated in the Tromsø Study in 1994-1995. Incident venous thromboembolic events during follow-up were registered up to September 1st, 2007. Results There were 447 venous thromboembolic events during a median of 12.5 years of follow-up. Multivariable hazard ratios per 5 % increment of hematocrit for the total population, adjusted for age, body mass index and smoking, were 1.25 (95 % CI: 1.08-1.44) for total venous thromboembolism and 1.37 (95 % CI: 1.10-1.71) for unprovoked venous throm-boembolism. In category-based analyses, men with a hematocrit in the upper 20th per