Background: Atrial fibrillation (AF) management guidelines recommend screening for symptoms of sleep-disordered breathing (SDB). We aimed to assess the role of self-reported daytime sleepiness in detection of patients with SDB and AF. Methods: A total of 442 consecutive ambulatory patients with AF who were considered candidates for rhythm control and underwent polysomnography comprised the study population. The utility of daytime sleepiness (quantified by the Epworth Sleepiness Scale [ESS]) to predict any (apnea-hypopnea index [AHI] ≥ 5), moderate-to-severe (AHI ≥ 15), and severe (AHI ≥ 30) SDB on polysomnography was tested. Results: Mean age was 60 ± 11 years and 69% patients were men. SDB was present in two-thirds of the population with 33% having moderate-to-severe SDB. Daytime sleepiness was low (median ESS = 8/24) and the ESS poorly predicted SDB, regardless of the degree of SDB tested (area under the curve: 0.48-0.56). Excessive daytime sleepiness (ESS ≥ 11) was present in 11.9% of the SDB population and had a negative predictive value of 43.1% and a positive predictive value of 67.5% to detect moderate-to-severe SDB. Male gender (odds ratio [OR]: 2.3, 95% confidence interval [CI]: 1.4-3.8, P = 0.001), obesity (OR: 3.5, 95% CI: 2.3-5.5, P < 0.001), diabetes (OR: 2.3, 95% CI: 1.2-4.4, P = 0.08), and stroke (OR: 4.6, 95% CI: 1.7-12.3, P = 0.002) were independently associated with an increased likelihood of moderate-to-severe SDB. Conclusions: In an ambulatory AF population, SDB was common but most patients reported low daytime sleepiness levels. Clinical features, rather than daytime sleepiness, were predictive of patients with moderate-to-severe SDB. Lack of excessive daytime sleepiness should not preclude patients from being investigated for the potential presence of concomitant SDB.