Background and Purpose-Stroke is very common, but computed tomography (CT) scanning, an expensive and finite resource, is required to differentiate cerebral infarction, hemorrhage, and stroke mimics. We determined whether, and in what circumstances, CT is cost-effective in acute stroke. Methods-We developed a decision tree representing acute stroke care pathways populated with data from multiple sources. We determined the effect of diagnostic information from CT scanning on functional outcome, length of stay, costs, and quality of life during 5 years for 13 alternative CT strategies (varying proportions and types of patients and rapidity of scanning). Results-For 1000 patients aged 70 to 74 years, the policy “scan all strokes within 48 hours” cost pound10 279 728 and achieved 1982.3 quality-adjusted life years (QALYs). The most cost-effective strategy was “scan all immediately” (pound9 993 676 and 1982.4 QALYs). The least cost-effective was “scan patients on anticoagulants and those in a life-threatening condition immediately and the rest within 14 days” (pound12 592 666 and 1931.8 QALYs). “Scan no patients” reduced QALYs (1904.2) and increased cost (pound10 544 000). Conclusion-Immediate CT scanning is the most cost-effective strategy. For the majority of acute stroke patients, increasing independent survival by correct early diagnosis, ensuring appropriate subsequent treatment and management decisions, reduced costs of stroke and increased QALYs.