Tumour necrosis factor-alpha (TNF-a) plays an important role in clot formation by activating platelets, monocytes and endothelial cells and inducing procoagulant substances such as negatively charged phospolipids or tissue factor. There is a genetically controlled inter-individual variation of TNF-a production. Carrying TNF2 allele could have a slight protective effect against the occurence of stroke in Sickle Cell Disease patients. We aimed to study this polymorphic site in Turkish children with the diagnosis of thrombosis.