In a prospective study of 200 patients with acute stroke, blood glucose and glycated haemoglobin (HbA1) were measured within 72 hours of onset. Unrecognized hyperglycaemia as defined by a raised stable HbA1 more than two s.d. above the mean reference value and no previous history of diabetes was present in 27%. No correlation existed between patient age and admission blood glucose or HbA1 levels (r = 0.1). Cumulative mortality and recovery of limb function was assessed in the first 136 patients with carotid distribution events. Admission blood glucose greater than or equal to 8 mmol/l was shown to be associated with a significantly greater mortality at 4 and 12 weeks (P less than 0.05). Multivariate analysis with age, glucose, HbA1 as independent variables demonstrated that age was the only significant predictor for death at 4 weeks (P less than 0.05) but at 12 weeks both age and blood glucose were significant (P less than 0.05). In patients less than 65 years blood glucose was a significant predictor for death (P less than 0.05) but in patients less than or equal to 65 years HbA1 and not glucose was significantly (P less than 0.05). Patients greater than or equal to 65 years with HbA1 greater than or equal to 7.5% were significantly more likely to have a raised admission blood glucose. Hyperglycaemia on admission was not shown to influence recovery of limb function. Increasing age is of greatest importance in predicting mortality although blood glucose is of prognostic value especially in the young stroke patient.