Thromboembolism is an important complication in children undergoing therapy for ALL as it has the potential to impact adversely on both their survival and quality of life. The incidence of thrombosis in children with ALL varies between 1.1% and 36.7% and the actual mean is 3.2%. The aim of our study is to review the available reported data on the effect of FVL on thrombotic risk in pediatric patients with acute leukemia.