Introduction: Early detection of atrial fibrillation (AF) after stroke is essential to achieve timely initiation of appropriate prophylactic treatment. We aimed to assess the diagnostic value of using prehospital continuous ECG (cECG) for AF detection after acute stroke. Patients and methods: In this retrospective cohort study, we included AF naïve ischemic stroke patients of 50 years or older. Medical records and corresponding digital prehospital cECGs were systematically reviewed. The proportion of AF detectable by prehospital cECG, in-hospital 12-lead ECG, telemetry and outpatient cECG was determined. McNemar's chi-squared test was used to compare probability of AF on prehospital cECG vs. in-hospital 12-lead ECG. Results: In 500 included patients, a new onset AF was detectable by prehospital cECG in 27 patients (5.4% [95% CI 3.6-7.8]). In-hospital 12-lead ECG detected AF in 28 of 458 patients (6.1% [95% CI 4.1-8.7). Sixty-two (12.4% [95% CI 9.6-15.6]) were diagnosed with new onset AF by either prehospital cECG, in-hospital 12-lead ECG, in-hospital telemetry or outpatient cECG. Thus, 43.5% of all AF cases were detectable during prehospital transport. The probability of AF did not differ between prehospital cECG and in-hospital 12-lead ECG. Nevertheless, a lack in overlapping diagnoses meant number needed to screening with prehospital cECG was 16 for diagnosing one AF case not detected by in-hospital 12-lead ECG. Conclusion: Using prehospital cECG as an addition to very early AF evaluation after acute stroke had diagnostic value and could represent a low cost and easily accessible opportunity for very early AF detection. This may improve post-stroke care and save resources for further unnecessary AF screening. Conducting routine prehospital cECG after acute stroke and ensuring this is available to clinicians is encouraged.