Venous thrombosis (VT) is a rare condition in childhood, being usually associated with congenital predisposition or acquired risk factors. The incidence of VT among children with cancer is between 1 and 36%. The highest incidence is among children with acute lymphoblastic leukaemia, followed by those with lymphoma and solid tumours. Malignancy and/or chemotherapy complications are considered as triggering factors. We report a case of a 15-year-old girl with non-Hodgkin lymphoma who developed generalized seizures during chemotherapy. Head computed tomography revealed right transverse and sagittal sinus thrombosis. Anticoagulation treatment using heparin as well as thrombolytic treatment with recombinant human tissue plasminogen activator (rhtPA) were introduced. The immediate application of rhtPA resulted in recanalisation of initially involved vessels which led to recovery with no neurological deficits. The reported case of severe venous thrombosis suggests that systemic treatment with rhtPA is effective and safe in children with cerebral venous sinus thrombosis.