Impaired fibrinolytic function, mainly due to an elevation of the plasma PAI-1 concentration, is a common finding in patients with thrombotic disease. Unfortunately, regarding patients with idiopathic deep vein thrombosis (DVT), no reliable prospective or genetic studies have been published. Concerning postoperative DVT, preoperatively increased PAI-1 level seems to predict a postoperative DVT in patients subjected to hip surgery. Several longitudinal cohort studies of patients with manifest coronary heart disease (CHD) have linked elevated plasma PAI-1 or tPA antigen concentrations to future cardiovascular events, particularly myocardial infarction. Before PAI-1 can be regarded as a risk factor in the conventional epidemiological sense, its relationship to myocardial infarction must be demonstrated in prospective studies of healthy populations. Regulation of the plasma concentration of PAI-1 is complex and at present not well understood. Multiple interactions with disturbances of both carbohydrate and lipoprotein metabolism are evident. Many studies have been carried out in cultured cells, but data can hardly be transformed into human pathophysiology. It seems that both environmental and genetic factors are of importance for the plasma PAI-1 concentration. Recently, knowledge of the importance of genetic factors involved in the regulation of plasma PAI-1 concentration has become available. Interestingly, preliminary data suggest that the 4G/5G polymorphism located within the PAI-1 promoter is connected to CHD. More data on larger patient groups are needed and will certainly shed new light on the importance of impaired fibrinolytic function in the etiology of CHD in the near future.