The aim of this study was to assess the plasma levels of von Willebrand factor antigen and ristocetin cofactor activity, which are well-known markers of endothelial function, in atrial fibrillation (AF) with or without mitral stenosis (MS). Forty-two patients (16 patients with MS and AF [MS(+)AF(+)], 13 patients with nonvalvular AF [MS(-)AF(+)], and 13 patients with MS and sinus rhythm [MS(+)AF(-)]) were included. Von Willebrand factor antigen levels and ristocetin cot, actor activities in all participants were assessed. Overall, von Willebrand factor antigen levels and ristocetin cofactor activities in the AF(+) patients were higher than in the AF(-) patients (P = .003 and P = .002, respectively). Von Willebrand factor antigen levels and ristocetin cofactor activities in the 3 groups were found to be different (P = .0.12 and P = .01, respectively). Von Willebrand factor antigen levels were similar between the MS(+)AF(+) and MS(-)AF(+) groups and were higher than that of the MS(+)AF(-) group. Ristocetin cofactor activity in the MS(-)AF(+) group Was significantly higher than in the other 2 groups. The ristocetin cofactor activity and von Willebrand factor antigen levels were significantly higher in diabetic or hypertensive patients than in nondiabetic or normotensive patients. According to the results of this study, circulating von Willebrand factor antigen levels and plasma ristocetin cofactor activities are affected by the presence of AF, MS, and associated comorbidities including type 2 diabetes mellitus and systemic hypertension. Further studies are needed to assess the role of von Willebrand factor antigen and ristocetin cofactor activity in predicting vascular thrombotic events in AF, MS, systemic hypertension, and diabetes mellitus.