Objective: Patients with silent and undiagnosed paroxysmal atrial fibrillation and flutter (AF) have increased risk of ischemic stroke. Patients with diabetes have a higher risk of both AF and ischemic stroke compared to patients without diabetes. Our aim was to investigate the prevalence of silent AF in patients with diabetes in an outpatient cohort and to identify the possible risk factors associated with AF. Research design and methods: This prospective observational study was performed in the outpatient diabetes clinic at a single University Hospital. We included 217 patients with type 1 or type 2 diabetes with at least one additional risk factor from the CHA₂DS₂VASc Score for Stroke Risk Assessment in Atrial Fibrillation. The primary outcome was prevalence of AF, with a duration of at least 30 s, recorded by a seven-day home-monitor, external loop recorder (ELR) in comparison to a standard resting ECG. Seventeen patients were excluded due to premature removal of the device. Results: In the final cohort of 200 patients the majority were male (58.5%) with a mean age of 66 ± 0.7 years. The mean BMI was 29 ± 6 and patients had a mean diabetes history of 23 ± 14 years with the majority diagnosed with type 2 diabetes (59%). Comorbidity was common with hypertension in 86%, and dyslipidemia in 80%. The total prevalence of silent AF [n = 20 (10%)] or flutter [n = 1 (0.5%)] was 10.5% using the ELR compared to a 0.0% detection-rate in the standard ECG method (p < 0.001). Higher age, male gender, albuminuria, and elevated systolic blood pressure were associated with AF in univariate analyses, but only age [OR 1.14 (95% CI = 1.00–2.04) (p = 0.048)], male gender [OR 4.9 (95% CI = 1.30–18.65) (p = 0.019)] and albuminuria [OR 2.7 (95% CI =1.08–6.98) (p = 0.034) were independently associated with AF. Mean CHA₂DS₂VASc Score was ≥2 (4.1, SD ± 1.6), and patients with AF were referred to further cardiac evaluation. Conclusion: Undiagnosed, silent AF is common in high-risk cohort with a long history of diabetes followed in a University Hospital outpatient clinic. Non-invasive monitoring with ELR enhances detection of AF and identifies candidates for early anticoagulation treatment with the possible effect of stroke prevention.