BACKGROUND: Recombinant tissue plasminogen activator (rT-PA) is an effective treatment for acute ischaemic stroke when given within 3h of symptom onset but can be delayed as patients wait for a diagnosis. The ROSIER assessment tool (Fig. 1) has been found to be effective in diagnosing stroke but to date has only been tested when used by doctors. OBJECTIVE: To compare registered nurses' ability to diagnose stroke using the ROSIER assessment tool with doctors' ability to diagnose stroke using traditional neurological assessment. DESIGN, SETTING, AND PARTICIPANTS: A prospective audit of all suspected stroke patients (n=106) admitted to the stroke unit of a district general hospital over an eight month period, assessed by registered nurses trained to use the ROSIER assessment tool to identify stroke. MAIN OUTCOME MEASURES: Time from admission to the stroke unit until initial assessment by doctors and registered nurses. Comparison of initial diagnosis by doctors and registered nurses with final diagnosis by a consultant for stroke. RESULTS: Of 106 suspected stroke patients, 78 (73.5%) had a final diagnosis of stroke or transient ischaemic attack (TIA) and 28 (26.4%) had an alternative diagnosis. Six patients with TIA were subsequently excluded as they were asymptomatic at the time of assessment, leaving 100 participants in the validation phase of the study. Using the ROSIER tool registered nurses achieved a diagnostic sensitivity for stroke of 98% (95% confidence interval 88-99), positive predictive value (PPV) 83% (95% confidence interval 73-90). Doctors using standard neurological assessment had a similar diagnostic sensitivity of 94% (95% confidence interval 86-98), PPV 80% (95% confidence interval 70-88). The mean time from initial assessment by registered nurses using the ROSIER tool, until assessment by doctor on the stroke unit was 75 min (SD=65.8 min). CONCLUSIONS: Registered nurses working on a stroke unit using the ROSIER assessment tool are able to diagnose stroke with a degree of accuracy comparable to doctors using clinical neurological assessment. Prompt assessment of suspected stroke patients by registered nurses using the ROSIER tool could reduce delays in eligible stroke patients being assessed for rT-PA treatment.