Thromboembolic events are an increasingly commonly recognized secondary complications in children treated for serious, life-threatening primary diseases. Nevertheless the incidence of venous thromboembolic disease remains 100 times less frequent in hospitalized children than hospitalized adults, as recent data suggest an incidence of 5,3/10.000 pediatric patients compared to an incidence of 2,5-5/100 in adult patients. Diseases usually associated with thromboembolic events in children are neoplasia, autoimmune or cardiac malformative disease. Contrarily to what is observed in the adult, the majority of deep vein thrombosis events occur at the upper limbs veins, usually at the place where devices for venous access like port-a-cath or central venous lines are inserted. Because of the relatively low incidence of venous thromboembolic events in children, the diagnostic approach used are largely extrapolated from guidelines obtained from adult studies. However, the diagnostic performances of some diagnostic tools like Doppler-Ultrasound are probably diminished in children. Moreover, the concept of developmental hemostasis, which stresses the point that the hemostatic system in children is quite different from the adult one, is widely accepted and clearly suggests that the diagnostic and therapeutic approach in pediatric patients may not be simply extrapolated from data obtained in adult studies. From a more practical point of view, the fact that the hemostatic system in children is a dynamic and evolving system, renders the therapeutic approach quite complex. In particular, doses of anticoagulants vary markedly across the pediatric age. The absence of adapted formulations of commonly used anticoagulants, for example the absence of liquid formulations of anti-vitamin K drugs, further complicates the administration and the correct monitoring of anticoagulation in children, and may diminish observance in adolescent patients. Even though the concept that "children are not little adults" is nowadays widely accepted, there is an urgent need for prospective studies to better assess the modalities of diagnosis and treatment of venous thromboembolic disease in this particular population.