The capsular warning syndrome (CWS) is a specific form of crescendo transient ischaemic attack (TIA) where the ischaemia is thought to be restricted to the region of the internal capsule due to in situ disease of a single penetrating artery. The stroke risk associated with CWS may be extremely high, although this has never been quantified against an appropriate control group. Forty-one consecutive cases of CWS who had not developed a fixed deficit before admission to a stroke unit were compared to 85 randomly selected patients with other forms of TIA admitted during the same period. The follow-up was from 1 to 14 years (mean 5.3 years). The stroke risk was significantly higher among CWS patients (11.1% per year) compared to other forms of TIA (2.7% per year) with an odds ratio of 3.5 (95% CI 1.7–7.2). The difference in stroke risk was most marked during the first 30 days when 32% of CWS patients reached this endpoint compared to only 1 % of controls. There was no difference in mortality during the follow-up period. All forms of therapy appeared to have little impact on outcome except for a reduced stroke rate for those controls still on aspirin therapy at the time of follow-up. The identification of patients with CWS as a pathophysiologically and prognostically distinct form of TIA has important implications for management and potential therapeutic interventio