A 9-year-old girl was admitted to our hospital with status epilepticus. Earlier in the day, she had complained of a headache and started vomiting. She then lost consciousness and began having a fit; the status epilepticus lasted 30 min and was stopped by phenobarbital. She had a congenital heart defect—truncus arteriosus with interventricular communication—which was surgically corrected a few days after birth. The girl was on long-term treatment with low-dose aspirin as the antiaggregant. She had no features of Marfan's or Ehlers–Danlos syndromes. Laboratory investigations showed leucopenia, low platelet count, and anaemia. Her C-reactive protein (CRP) was 45 mg/L and her erythrocyte sedimentation rate (ESR) was 50 mm/h. Her liver enzymes were also slightly raised. A CT scan of her brain showed an intraparenchymal haematoma and intraventricular haemorrhage. Three-vessel arteriography showed a right Sylvian artery aneurysm (figure). Successive blood cultures and broad-range 16S recombinant DNA PCR—as well as PCR for herpes simplex viruses 1–5—were all negative. At this stage, our working diagnosis was endocarditis leading to the mycotic cerebral aneurysm, despite no signs of a fever. We drained the haematoma and commenced treatment with antibiotics; 2 days later, we embolised the aneurysm. The patient recovered and had a mild, left-sided hemiparesis when she left hospital after 4 weeks.