Apart from being an acute phase reactant, fibrinogen appears to play an important although not widely recognized role in athero-/thrombogenesis. Arteriosclerotic diseases are associated with elevated levels of plasma fibrinogen. Strategies that lower the cardiovascular risk also lower fibrinogen levels. Virtually all accepted risk factors are associated with hyperfibrinogenaemia, while low risk populations usually have low fibrinogen levels. Epidemiological studies show that fibrinogen is a predictor of arteriosclerotic diseases. Its predictive power seems to be as high as or higher than accepted risk factors. These findings and other circumstantial, as well as experimental, evidence suggest that fibrinogen is a powerful, independent cardiovascular risk factor.