A 25-year-old man had granulomatous angiitis of the CNS. The disease began with symptoms of an upper respiratory tract infection; it had a relentless course, simulating viral encephalitis, with the patient dying some six months after the onset of symptoms. The lesions were confined to small intracranial arteries and veins, predominantly about the cerebellum. An unusual feature was the occurrence of a small (2 mm) aneurysm on a leptomeningeal artery deep in a cerebellar sulcus. There is a need for pooling data and pathological material by an international body to enable detailed expert analysis of large numbers of cases of cerebral angiitis that do not now constitute a homogeneous group.