BACKGROUND AND OBJECTIVES: Coffee is one of the most popular beverages in the world. Caffeine is one of the substances contained in coffee and it is well known to increase blood pressure and the peripheral vascular resistance, in part because it stimulates the sympathetic nervous system. Arterial stiffness is an important factor for the performance of the cardiovascular system and it is an independent prognosticator of cardiovascular disease. We investigated the acute effect of caffeine on arterial stiffness in young healthy subjects. SUBJECTS AND METHODS: We enrolled 20 young healthy subjects, who were randomly divided two groups. The caffeine group (10 subjects, 4 males, mean age: 23.3+/-1.1 years) received 520 mL caffeinated coffee and the control group (10 subjects, 4 males, mean age: 23.1+/-1.3 years) received 520 mL water. The arterial stiffness was evaluated by the carotid-radial pulse wave velocity and the augmentation index as corrected by heart rate (75 bpm), and all the hemodynamic measurements were obtained at baseline, 30, 60, 120 and 180 minutes after ingestion of the coffee or water. RESULTS: Arterial stiffness measured by carotid-radial pulse wave velocity increased progressively from 9.4+/-1.2 m/sec at baseline to 11.5+/-1.6 m/sec (p<0.05) at 30 minutes after the coffee intake. In addition, peripheral systolic pressure increased progressively from 107.1+/-10.2 mmHg at baseline to 114.4+/-12.9 mmHg (p<0.05) at 60 minutes after the coffee intake. Such changes were not seen in control group. CONCLUSION: Caffeine affects increased the pulse wave velocity and systolic blood pressure. This means that coffee might have an adverse effect on arterial stiffness.