witness response at acute onset of stroke a qualitative theoryguided study background delay in calling emergency medical services following stroke limits access to early treatment that can reduce disability emergency medical services contact is mostly initiated by stroke witnesses often relatives rather than stroke patients this study explored appraisal and behavioural factors that are potentially important in influencing witness behaviour in response to strokemethods and findings semistructured interviews with 26 stroke witnesses were transcribed and theoryguided content analysed was undertaken based on the common sense selfregulation model appraisal processes and theory domains framework behavioural determinants response behaviours were often influenced by heuristicsguided appraisal ie mental rules of thumb some witnesses described their responses to the situation as automatic and instinctive rather than products of deliberation potential behavioural influences included environmental context and resources eg time of day social influence eg prompts from patients and beliefs about consequences eg 999 accesses rapid help findings are based on retrospective accounts and need further verification in prospective studiesconclusions witnesses play a key role in patient access to emergency medical services factors that potentially influence witnesses responses to stroke were identified and could inform behavioural interventions and future research interventions might benefit from linking automaticinstinctive threat perceptions with deliberate appraisal of stroke symptoms prompting action to call emergency medical services