To determine the natural history of deep vein thrombosis in children presented with a first episode in the lower extremity veins.

Children with objective diagnosis of acute deep vein thrombosis were followed up with ultrasound and clinical examination. Risk factors and clinical presentation were prospectively collected. The prevalence of recurrent deep vein thrombosis and the development of signs and symptoms of chronic venous disease were recorded.

There were 27 children, 15 males and 12 females, with acute deep vein thrombosis, with a mean age of 4 years, range 0.1–16 years. The median follow-up was 23 months, range 8–62 months. The location of thrombosis involved the iliac and common femoral vein in 18 patients and the femoral and popliteal veins in 9. Only one vein was affected in 7 children, two veins in 14 and more than two veins in 6. Recurrent deep vein thrombosis occurred in two patients, while no patient had a clinically significant pulmonary embolism. Signs and symptoms of chronic venous disease were present at last follow-up in 11 patients. There were nine patients with vein collaterals, but no patient developed varicose veins. Reflux was found in 18 veins of 11 patients. Failure of recanalization was seen in 7 patients and partial recanalization in 11. Iliofemoral thrombosis (p = 0.012) and failure to recanalize (p = 0.036) increased significantly the risk for developing signs and symptoms.

Children with acute proximal deep vein thrombosis develop mild chronic venous disease signs and symptoms at mid-term follow-up and are closely related with iliofemoral thrombosis and failure to recanalization.