To study the possible risk factors for cardiovascular disease, we collected data on plasma levels of coagulation factors, blood pressure, serum cholesterol, and smoking in a random sample of 792 men 54 years of age. During 13.5 years of follow-up, myocardial infarction occurred in 92 men, stroke in 37, and death from causes other than myocardial infarction or stroke in 60. The blood pressure, degree of smoking, serum cholesterol, and fibrinogen level measured at the base-line examination proved to be significant risk factors for infarction by univariate analyses during follow-up, and blood pressure and fibrinogen were risk factors for stroke. Fibrinogen and smoking were strongly related to each other. The relation between fibrinogen and infarction, and between fibrinogen and stroke, became weaker when blood pressure, serum cholesterol, and smoking habits were taken into account, but was still significant for stroke. Although causality cannot be inferred from these data, it is possible that the fibrinogen level plays an important part in the development of stroke and myocardial infarction.