Various abnormalities of hemostasis have been described in obesity, mainly concerning increased levels of plasminogen activator inhibitor-1, but other abnormalities of coagulation and platelet activation have been reported as well. Circulating microparticles have also been observed in obese patients. These suggest that obesity would be a risk factor for venous thromboembolism (VTE). Analysis of the database of the National Hospital Discharge Survey showed compelling evidence that obesity is, in fact, a risk factor for VTE. Obesity is also a risk factor for recurrent VTE. A synergistic effect of oral contraceptives with obesity has been shown.