Diagnosis of paroxysmal atrial fibrillation (AF) in stroke patients is challenging, but highly clinically relevant. The percentage of stroke patients with permanent AF increases with age, but limited data are available for the age-dependent yield of paroxysmal AF by Holter monitoring. Patients with acute cerebral ischemia were included into the prospective observational Find-AF study. Patients free from AF at presentation received 7 day Holter monitoring. We calculated the percentage of otherwise undetected paroxysmal AF and the number needed to screen for age groups under 60 years, and in 5 year clusters from the age of 60 up to 85 and older. 272 patients were included, 43 (15.8 %) had AF at admission, 33 patients with paroxysmal AF were identified by 7 day Holter (n = 29) or medical history (n = 4).The yield of 7 day Holter ECG clearly increased with older age (p = 0.004): <60 years: 5 %, 60-64 years: 5 %, 65-69 years: 7 %, 70-74 years: 11 %, 75-79 years: 13 %, 80-84 years: 25 %, ≥ 85 years: 39 %. The number needed to screen (NNS) to find one patient with paroxysmal AF decreased with age: ≤ 60 years: 18, 60-64 years: 20, 65-69 years: 14, 70-74 years: 9, 75-79 years: 8, 80-84 years: 4, ≥ 85 years: 3, respectively. In patients <65 years, all AF cases were detected by Holter ECG. The percentage of paroxysmal AF in stroke patients increases with age. The 7 day Holter ECG is most efficient in elderly patients.