The authors determined von Willebrand factor (vWF) in 63 persons with migraine, 11 persons with migraine and prior stroke, and 35 frequency-matched controls. Additional studies were done in a subset with migraine without aura who were headache free for >7 days. Migraineurs with prior stroke had significantly higher vWF antigen (170% versus 106%) and activity (162% versus 108%) than the control group. vWF antigen (126%) and activity (130%) were also significantly higher in migraineurs without stroke. Multimers and protease activity were normal in the interictal subset.