Idiopathic intracranial hypertension (IIH) is characterised by increased intracranial pressure with normal cerebrospinal fluid, and no evidence of space occupying process, meningeal pathology or venous thrombosis. The condition is associated with obesity, especially in women of childbearing age. IIH is a rare but serious cause of headache, and constitutes a differential diagnosis for sudden-onset headache, particularly if the patient has visual disturbances not related to migraine and reports pulsatile tinnitus, cranial nerve palsy or radiculopathy.