['The circle of Willis (CoW) is a primary collateral pathway that compensates quickly for a drop in cerebral blood flow. Using the complete CoW as a surrogate marker for good collateral circulation, its prognostic value after intravenous thrombolysis was examined.', 'We prospectively studied 64 consecutive patients with acute ischemic stroke treated with tissue plasminogen activator within 3 hours of stroke onset between October 2005 and June 2012 in our hospital. The study protocol was based on standard guidelines for intravenous thrombolysis. On computed tomographic angiography 24 hours after thrombolysis, the CoW was complete in 21 (32.8%) cases and incomplete in 43 (67.2%).', 'Patients with complete CoW were more likely to have early improvement in National Institute of Health Stroke Scale (NIHSS) score (median improvement 2 vs 0 at 2 hours; 4 vs 1 at 24 hours), be independent at 3 months (42% vs 19%). In the incomplete CoW group, the rate of symptomatic intracerebral haemorrhage (SICH) according to the Safe Implementation of Thrombolysis in Stroke-Monitoring Study (SITS-MOST) definition was almost 3 times higher. Complete CoW was one of the strongest predictors of good functional outcome at 3 months (odds ratio 2.32; P = .01).'] Is configuration of the circle of Willis associated with less symptomatic intracerebral hemorrhage in ischemic stroke patients treated with intravenous thrombolysis?