SummaryA boy (age: 71/12 years) with acute lymphoblastic leukaemia developed thrombosis of the sinus sagitalis superior with secondary haemorrhagic infarction while on induction treatment with vincristine, prednisone, and asparaginase. Based on this report, the potential pathogenic mechanisms are discussed with respect to congenital prothrombotic defects as well as to the role of antileukaemic treatment. Current hypotheses on mechanisms for thromboembolism in children and proposed prophylactic strategies are briefly summarized.