Henoch-Schonlein purpura (HSP) is the most common systemic vasculitis in children. Although long-term outcome is generally good, serious complications may occur. Thrombosis has been reported only as an extremely rare complication of HSP. Here, we describe a 15-year-old-boy with features of HSP, who developed left main iliac, external iliac and femoral vein thrombosis. Factor VIII (FVIII) and homocystein levels were found to be high. This suggests that HSP itself may lead to a prothrombotic state and increase the risk of developing thrombosis in patients who have any risk factors.