Thromboembolism of the vena cava, the venae iliaca communis, externa, femoralis, poplitea, and the fibular vein group of the left lower limb was diagnosed in a 13 year old girl. Several thrombogenic risk factors (APC-resistence, homocystinuria, contraception, smoking) were identified. Due to painful symptoms and for prevention of postthrombotic syndrome continuous systemic thrombolysis with rt-PA (0,5 mg/kg/d), in addition to heparine, was performed for 6 days. Diagnostic imaging at the end of therapy demonstrated complete and partial recanalization of the vena cava inferior, venae iliaca communis and externa. The distal veins of the leg remained occluded. After catheterization of the internal jugular vein and placement of a cava filter only mild pulmonary embolism occurred during systemic thrombolysis. No further complications were observed. All in all, therapy was tolerated well. Systemic thrombolysis with rt-PA in children and adolescents, although not established for regular treatment, is an effective therapeutic option in severe venous thrombosis.