Red blood cell distribution width (RDW) is an inexpensive marker of anisocytosis easily available in the standard complete blood cell count. Besides its traditional use in the differential diagnosis of anemias, RDW values reflect abnormalities in erythropoiesis and red blood cell metabolism related to aging, sex, ethnicity, systemic inflammatory state, and oxidative stress. Thus, higher RDW values are common findings in several acute clinical conditions and chronic diseases. Increasing evidence suggests a prognostic role of higher RDW levels in many cardiovascular diseases. Among them, we aimed to review current literature focusing on the possible relation between RDW and atrial fibrillation (AF). Since aging, inflammation, and atrial substrate remodeling have a well-established role in AF pathogenesis, AF burden, and patient prognosis, we analyzed available data exploring the possible use of RDW in identifying patients at higher risk of AF and as a biomarker of worse outcomes for AF patients.