From August 1987 through December 1989 all consecutive conscious patients younger than 70 years with a recent (less than 48 h) brain infarction of the carotid territory were prospectively included in the study. Blood samples for fasting blood glucose and glycosylated haemoglobin (HbA1c) were taken after a median delay of 23 h of the onset of symptoms. The severity of hemiparesis was assessed on admission, at 1 week, 3 weeks, and 3 months. The functional outcome was assessed at 3 months. Computed cerebral tomography was performed on admission, and later on at 3 weeks or 3 months. The brain infarct volume was measured from the CTs. The patients were diagnosed to have prestroke normoglycemia (n = 76) and prestroke hyperglycemia (n = 23) on basis of the HbA1c level. The case fatality rate, severity of hemiparesis, functional outcome, and infarct size did not differ between these 2 groups. On the other hand, fasting blood glucose level of the non-diabetics correlated strongly with the severity of hemiparesis and predicted stroke outcome. A statistically significant correlation was observed between blood glucose values and the volumes of cortical infarcts in non-diabetics. Because prestroke blood glucose level, in contrast to post-stroke blood glucose level, did not have any predictive value concerning stroke outcome it is concluded that high fasting blood glucose values after stroke reflect a stress response to a more severe ischemic brain lesion.