A 36-year-old man with a 21-year history of Crohn's disease suddenly developed left hemiparesis. He did not have atherosclerotic risk factors on admission, but he had marked dehydration which was likely due to prolonged home intravenous hyper-alimentation. Brain MRI revealed lacunar infarction in the right anterior corona radiata. An anticoagulation drug and a free-oxide scavenger successfully reversed his neurological deficits almost completely. Stroke in young adults less than 40 years old is extremely rare; therefore, we conclude that Crohn's disease can be a risk factor for acute ischemic stroke in our case, due most probably to dehydration and other complex mechanisms.