Purpose: Atrial fibrillation (AF) is associated with an increased risk of mortality and stroke. However, few prospective studies have examined the association of smoking and drinking on AF in Western populations. No studies have examined the two combined effects on the risk of AF. We assessed the combined effect of smoking and drinking status on the risk of incident AF in a 12.6-year prospective study of an urban general population in Japan. Methods: A total of 6,798 participants (30 to 79 years old) in the Suita Study were initially free of AF and prospectively followed up for incident AF. Participants were diagnosed with AF if AF or atrial flutter was present on an electrocardiogram from a routine health check-up examination (every 2 years) or if AF was indicated as a present illness by questionnaires or by registration of cardiovascular disease events during follow-up. Smoking status was classified into 3 categories: nonsmokers and former and current smokers. Alcohol consumption was classified into 5 categories: nondrinkers and former and current drinkers, which were divided into further three categories: weekly alcohol consumption of 1 to 160 g/week (moderate drinkers; <1 gou/day in average, a Japanese unit), 161 to 321 g/week, and ≥322 g/week (excessive drinkers; ≥2 gous/day). Blood pressure (BP) categories were defined by the following criteria: optimal, normal, and highnormal BP, and hypertension. Cox proportional hazard ratios (HRs; 95% confidence intervals, CIs) were analyzed after adjusting for age, sex, BP categories, diabetes, hyperlipidemia, body mass index, (and smoking and drinking status) at baseline. Results: During 12.6 years of follow-up, 237 incident AF events occurred (4.05 and 1.68 per 1,000 person-years for men and women, respectively). Compared with nonsmokers, the adjusted HR (95% CIs) of incident AF for smokers was 1.46 (1.00 to 2.12). Adjusted hazard ratio for AF was 1.14 (1.02 to 1.28) per 10 cigarettes a day. Compared with nondrinkers, the adjusted HRs (95% CIs) of incident AF for moderate and excessive drinkers were 1.00 (0.70 to 1.41) and 1.63 (1.05 to 2.53), respectively. Compared with nonsmoker with non-excessive drinking, the adjusted HRs (95% CIs) of incident AF for smokers with non-excessive drinking and nonsmokers and smokers with excessive drinking were 1.42 (1.01 to 1.98), 1.97 (1.17 to 3.32), and 2.07 (1.27 to 3.37), respectively. Conclusions: Cigarette smoking and excessive drinking are important risk factors for incidence of AF. Lifestyle modifications for moderate drinking and smoking cessation are important for preventing AF in general population.