Objective: To determine whether raised plasma glucose concentration independently influences outcome after acute stroke or is a stress response reflecting increased stroke severity. Design: Long term follow up study of patients admitted to an acute stroke unit. Setting: Western Infirmary, Glasgow. Subjects: 811 patients with acute stroke confirmed by computed tomography. Analysis was restricted to the 750 non-diabetic patients. Main outcome measures: Survival time and placement three months after stroke. Results: 645 patients (86%) had ischaemic stroke and 105 patients (14%) haemorrhagic stroke. Cox's proportional hazards modelling with stratification according to Oxfordshire Community Stroke Project categories identified increased age (relative hazard 1.36 per decade; 95% confidence interval 1.21 to 1.53), haemorrhagic stroke (relative hazard 1.67; 1.22 to 2.28), time to resolution of symptoms >72 hours (relative hazard 2.15; 1.15 to 4.05), and hyperglycaemia (relative hazard 1.87; 1.43 to 2.45) as predictors of mortality. The effect of glucose concentration on survival was greatest in the first month. Conclusions: Plasma glucose concentration above 8 mmol/l after acute stroke predicts a poor prognosis after correcting for age, stroke severity, and stroke subtype. Raised plasma glucose concentration is therefore unlikely to be solely a stress response and should arguably be treated actively. A randomised trial is warranted. A plasma glucose concentration above 8 mmol/l after acute stroke predicts poorer chances of survival and independence This effect of raised glucose concentration persists after adjusting for factors known to affect the outcome of stroke–namely, age, stroke type, and stroke severity A clinical trial of active control of plasma glucose concentration is warranted