Iron deficiency anaemia is a common disorder in the paediatric age-group. The association between iron deficiency and venous thrombosis in children without an underlying illness is rare. Two cases are described. A 17-year-old girl had been taking oestrogen-progestogen therapy for contraception for about 2 years and developed a lower-limb deep vein thrombosis associated with pulmonary embolism. A 3-year-old girl was admitted to the paediatric emergency department with pallor, weakness and vomiting, and a cerebral CT showed a recent cerebral venous thrombosis. Both cases had severe iron-deficiency anaemia which increases a thrombotic tendency and could be a further crucial trigger of venous thrombosis in patients at low risk; therefore, in cases of unexplained thrombosis, it must always be considered to be a risk factor. APCR: activated protein C resistance; CMV: cytomegalovirus; CT: computerised tomography; CVST: cerebral venous sinus thrombosis; CVT: cerebral venous thrombosis; DVT: deep vein thrombosis; DOACs: direct oral anticoagulants; EBV: Epstein-Barr virus; ID: iron deficiency; IDA: iron deficiency anaemia; LMWH: low molecular weight heparin; PE: pulmonary embolism; RDW: red blood cell distribution width; VT: venous thrombosis.