Congenital anomalies of the inferior vena cava (WC), such as absence or atres ia, although well documented, are uncommon and result from aberrant development during embryogenesis. Absence or atresia of the IVC is usually discovered accide ntally. Patients are typically asymptomatic of the condition itself. Many concur rent cardiovascular- associated abnormalities have been described. We report a 10- y- old boy admitted to the emergency room with painful swelling of his rig ht lower limb without previous trauma or surgery. After 3 d, swelling also invol ved the left lower limb. A Doppler ultrasound of the lower limbs revealed bilate ral thrombosis of the vena iliaca communis, vena iliaca externa, femoral vein co mmunis and superficial extending to the IVC.Magnetic resonance imaging (MRI) of the abdomen was performed. On MRI, we demonstrated a hypoplastic WC. The results of blood coagulation studies, including levels of antiphospholipid antibodies, proteins C and S, and antithrombin III, were normal. The patient was treated wit h intravenous heparin for 8 d and discharged with oral warfarin therapy, which h as been recommended for life. Conclusion: Therapy against deep venous thrombosis must be focused on its prevention in the future. An abnormal inferior vena cava should be considered in young patients with deep venous thrombosis without appa rent cause. Congenital anomalies of the inferior vena cava (WC), such as absence or atres ia, although well documented, are uncommon and result from aberrant development during embryogenesis. Patients are typically asymptomatic of the We report a 10- y- old boy admitted to the emergency room with painful swelling of his rig ht lower limb without previous trauma or surgery. After 3 d, swelling also involuntary ved the left lower limb. A Doppler ultrasound of the lower limbs revealed bilate ral thrombosis of the vena iliaca communis, vena iliaca externa, femoral vein co mmunis and superficial extending to the IVC. Magnetic resonance imaging (MRI) of the abdomen was performed. On MRI, we demonstrated a hypoplastic WC. The results of blood coagulation studies, including levels of antiphospholipid antibodies, proteins C and S, and antithrombin III, were normal. The patient was treated wit h intravenous heparin for 8 d and discharged with oral warfarin therapy, which h as been recommended for life. Conclusion: Therapy against deep venous thrombosis must be focused on its prevention in the future. cava should be considered in young patients with deep venous thrombosis without appa rent cause.