The authors revised the published data on coagulation abnormalities observed in patients suffering from primary vascular diseases or vasculitides associated with systemic diseases of the connective tissue. These patients present a tendency toward thrombosis as a result from platelet activation and endothelial cell injury, together with altered fibrinolytic activity. The proliferative events secondary to platelet activation and endothelial injury remain present after cessation of the inflammatory process and may play a role at the end stage obstruction of the vascular lumen always seen in these diseases.