Objectives: We assessed the prevalence of atrial fibrillation (AF) prior to first-ever ischemic stroke by examining a comprehensive electronic ECG archive. Methods: The study sample comprised 336 consecutive stroke patients (median age 76 (IQ16) y, 200 men) enrolled in Lund Stroke Register from March 2001 to February 2002 and 336 age- and gender-matched controls without stroke history. AF prior to admission was studied using the regional electronic ECG database and record linkage with the National Swedish Hospital Discharge Register (SHDR). Medical records were reviewed for AF documentation and CHA₂DS₂-VASc risk score. Results: Atrial fibrillation before or at stroke onset was detected in 109 (32.4%) stroke patients and 44 (13.1%) controls, P < 0.001. Twenty-five of 109 stroke patients had AF detected only on previous ECG (n = 14) or through the SHDR (n = 11). The most prevalent type of AF in stroke group was non-permanent AF (59.6%). AF prevalence among patients admitted with sinus rhythm at hospital admission (n = 266) was higher in those with CHA₂DS₂-VASc score ≥ 6 (28.6%) than with CHA₂DS₂-VASc score < 6 (13.0%), P = 0.043. Conclusion: Comprehensive approach for AF screening allows detecting AF in one-third of patients admitted with first-ever ischemic stroke. Patients with high cardiovascular risk are more likely to have non-permanent AF.