Background—Recent genetic animal models reveal important roles of platelet P-selectin on progression of atherosclerosis. In the present study, we examine the relation between platelet P-selectin expression and atherosclerotic parameters in 517 subjects.Methods and Results—Unrelated subjects (n=517; 235 male and 282 female), including 187 with type 2 diabetes, 184 with hypertension, and 366 with hyperlipidemia, were enrolled in the study. P-selectin expression was determined by whole-blood flow cytometry. Arterial stiffness (stiffness index &bgr;) and arterial wall thickness (intima-media thickness [IMT]) were determined by carotid ultrasound. P-selectin expression was significantly and positively correlated with carotid IMT and stiffness index &bgr;. Multiple regression analyses showed that the association of the percentage of P-selectin–positive platelets with carotid IMT was independent of other clinical factors. Moreover, the percentage of P-selectin–positive platelets was higher in subjects with carotid plaque and was an independent factor associated with occurrence of carotid plaque analyzed by multiple logistic regression analysis. Finally, the percentage of P-selectin–positive platelets was positively associated with age, body mass index, systolic and diastolic blood pressure, and HbA1c and inversely associated with HDL cholesterol.Conclusions—Platelet P-selectin is independently associated with atherosclerotic arterial wall changes in human subjects.