A 27-year-old woman with a history of aplastic anaemia complained of poor control of her right arm and hand, unsteady gait, and headache that increased while in a recumbent position. She was diagnosed with cerebral sinus thrombosis. Additional investigation revealed paroxysmal nocturnal haemoglobinuria (PNH). Treatment with heparin was initiated but stopped after the patient developed a brain haemorrhage. The patient recovered with no signs of residual symptoms and began taking oral anticoagulants as maintenance therapy. PNH is a rare acquired clonal disorder due to a defective expression of the glycosylphosphatidyl-inositol anchor membrane protein. It is characterised by haemolytic anaemia, diminished haematopoiesis, increased susceptibility for infections and a hypercoagulable state. Patients with aplastic anaemia have an increased risk of developing PNH. In patients with cerebral sinus thrombosis PNH should be considered as a possible underlying disorder. These patients should be questioned for possible clinical symptoms of PNH, such as acute abdominal pain or dark urine in the morning. For patients with these symptoms and in those with a history of aplastic anaemia or recurrent thrombosis, additional testing for PNH should be conducted.