All newly diagnosed patients with a first radiologically confirmed thrombotic event (any site) diagnosed at Children's Medical Center, Dallas will be followed prospectively with global coagulation assessment over a 24-month period, and monitored for development of carefully defined adverse VTE outcomes in a blinded manner. Biomarker assessment will include global coagulation assays (thrombin generation assay and modified thromboelastography to study fibrinolysis) at 3, 6, 12, 18 and 24 months post VTE diagnosis.