Background Oral anticoagulation is highly effective in preventing stroke and mortality in nonvalvular atrial fibrillation patients. However, the efficacy and safety of vitamin K antagonists (the main oral anticoagulation drug used) strongly depends upon the quantity of anticoagulation control, as reflected by the average percentage of the time in therapeutic range of international normalized ratio 2.0-3.0. An easy, simple prediction of which atrial fibrillation patients are likely to do well on vitamin K antagonists (with good average time in therapeutic range) could guide decision-making between using vitamin K antagonists (eg, warfarin) and non-vitamin K antagonist oral anticoagulants. Methods and Results In a consecutive cohort of nonvalvular atrial fibrillation patients attending our anticoagulation clinic, we tested the hypothesis that the new Sex, Race, Medical history, Tobacco use, Race (SAMe-TT2R2) score was a predictor for good average time in therapeutic range, and second, this would translate into adverse events in a “real world” cohort of patients with nonvalvular atrial fibrillation. The incidence of bleeding, adverse cardiovascular events (including stroke/thromboembolism), and mortality during the follow-up was higher with increasing SAMe-TT2R2 score. The SAMe-TT2R2 score was predictive for the composite of all adverse events (hazard ratio 1.32 [95% Confidence Interval 1.17-1.50]; P <.001), adverse cardiovascular events (1.52 [1.28-1.83]; P <.001), and all-cause mortality (1.41 [1.16-1.67]; P = .001). A trend was also observed for major bleeding events (1.23 [0.99-1.53]; P = .059). Conclusion In a “real world” cohort of consecutive patients with nonvalvular atrial fibrillation, a high SAMe-TT2R2 score (reflecting poor anticoagulation control with poor time in therapeutic range) was associated with more bleeding, adverse cardiovascular events, and mortality during follow-up.