To examine the risk factors related to the incidence of aortic stiffness, 1,045 Japanese men aged 40 to 54 years with aortic pulse wave velocity (PWV) of less than 8.0 m/sec were followed up for seven years with annual examinations, with an average period of observation of 6.3 years with standard deviation of 1.56 years. Subjects who showed 8.0 m/sec and over of PWV during follow-up surveys were defined as incidental cases of aortic stiffness. Kaplan-Meier analysis showed that die incidence of aortic stiffness increased significantly with increases in age, body mass index, and total cholesterol and low-density lipoprotein (LDL) cholesterol levels. The incidence of aortic stiffness was significantly higher among those who had or currently smoked than among those who never smoked. From multivariate analysis using Cox proportional hazards model, the incidence of aortic stiffness showed a significant dose-response relationship for age, PWV, total cholesterol and LDL cholesterol levels and smoking habits. These results indicate that increased levels of total cholesterol and LDL cholesterol and smoking habits may constitute contributing factors for the development of aortic stiffness in middle-aged Japanese men.