This chapter focuses on hemorrhages occurring at the base of the brain, because extravasation at the convexity of the brain is associated with few symptoms and signs, if any at all. The vast majority (85%) of spontaneous hemorrhages in the subarachnoid space at the base of the brain are caused by aneurysms. The key feature in diagnosing subarachnoid hemorrhage (SAH) is the history of sudden, severe, and unusual headache. Sudden onset headache may also occur with other intracranial hemorrhages, with non-hemorrhagic brain disease, and especially with innocuous forms of thunderclap headache: variants of vascular headache, migrainous or not, or of muscle contraction headache. Sentinel headaches, previous episodes of sudden headache, are generally believed to be common in patients with aneurysmal SAH. The chapter talks about neck stiffness, anosmia, subhyaloid hemorrhages, third cranial nerve palsy, parinaud's syndrome, cerebellar signs, monoparesis, and parkinsonism.