The natural course of 365 random patients with peripheral arterial obliterative disease was followed up on an average 8 years. In 36% of the patients worsening of angiological condition has been shown. The state of the other patients was unchanged (55%) or improved (9%). During the observation period 87 angiological surgeries and amputation of 41 lower limbs were performed, most of them in 1-2 years after onset of the disease. At follow up in 151 cases myocardial infarction and in 72 cases stroke occurred; the incidence of both diseases was characterized by a cluster like accumulation in 1-3 years before or after onset of the disease. The deterioration of the angiological condition of the patients was related to smoking (mainly heavy smoking), diabetes mellitus and-even more markedly--to the combinations of different risk factors including smoking. The pathological levels of haemorheological factors also showed significant connection with the severity of the disease. In the prospective 6 year period of the study 147 patients (40%) died. This mortality was twice that of the general population matched for age and sex. Information about the cause of death could be collected in 128 cases (87%), among them 51 (40%) died of vascular diseases (peripheral arterial obliterative disease, myocardial infarction, stroke).