BACKGROUND: Benefits of reperfusion therapies in acute ischemic stroke are highly time-dependent. It is crucial that people who witness the onset of symptoms call emergency medical services (EMS) immediately. The aim of this study was to examine whether there is a gap between recognition of stroke and responding correctly by calling EMS using a scenario-based measure. METHODS: Population-based survey of 1406 individuals from Newcastle upon Tyne, UK, examining stroke recognition and response knowledge using 12 scenario-based vignettes. The response rate was 32% out of 5000 contacted individuals. In total, 16,574 responses to scenarios were examined to investigate whether respondents would recognise stroke symptoms and indicate to call EMS immediately. RESULTS: In 16% of cases people recognised stroke but did not correctly respond by indicating to call EMS. In 49% of responses people recognised stroke and would respond correctly, while in 31% of cases people both failed to correctly recognise and failed to identify the correct response to the stroke scenario. In 5% of cases stroke was not identified but a correct response was indicated. When stroke was recognised, in 25% of responses people indicated that they would not call EMS. Recognition self-efficacy and response self-efficacy were associated with correct response. CONCLUSIONS: A recognition-response gap was identified among UK adults in hypothetical scenarios concerning stroke. Both recognition and translation to adequate EMS response should be explicitly addressed in interventions aiming to improve witness response to stroke. Self-efficacy may be a promising target to close the recognition-response gap.