OBJECTIVES: Although studies have investigated the epidemiology of patients with atrial fibrillation (AF), research in Japan is lacking. The aim of the current study was to assess the patient characteristics, medication use, and comorbidities of an AF sample from a representative data source in Japan to make broad cross-region comparisons. METHODS: The 2008, 2009, and 2010 Japan National Health and Wellness Survey (NHWS) datasets were used in this study. The NHWS is an Internet-based survey administered to the adult population in Japan using a random stratified sampling framework to ensure demographic representativeness. Only patients who reported a diagnosis of AF (N=565) in these datasets were included in the analyses. Demographics, health characteristics, stroke risk (using the CHA2DS2-VASc score), and comorbidities were all assessed.  RESULTS: Most patients were male (83.5%), 60 years or older (77.0%), weighed 64.50 kilograms (SD=11.04), and had been diagnosed for 10.4 years (standard deviation=10.6). Nearly a fifth (19.1%) continued to smoke. Based on the CHA2DS2-VASc score, 11.5% patients were of low stroke risk, while 35.4% and 53.1% were of moderate and high risk, respectively. Despite this risk for stroke, only 64.2% of patients were currently being treated for AF. Patients with AF also reported a number of comorbidities including 87.1% with another cardiovascular condition, 67.8% with a urological condition, 37.3% with dyspepsia, and 32.7% with pain. A total of 8.0% of patients reported a previous myocardial infarction. CONCLUSIONS: The AF population in Japan is somewhat unique in its dramatic gender split and lower body weight. Additionally, most AF patients in Japan, through a combination of their behaviors (e.g., smoking) and health characteristics, are at moderate-to-high risk for a future stroke. Despite this risk, not all patients are being treated according to current guidelines. Further, these patients suffer from a number of comorbidities which can complicate treatment decisions.