In contrast to the knowledge on the frequency and determinants of arterial diseases, little epidemiologic research has been carried out on venous diseases; this may be partly due to methodological problems in defining chronic venous insufficiency and in measuring these conditions with sufficient validity. Epidemiologic studies that were published after 1965 and that are not based on clinical series are reviewed; prevalence and incidence rates are reported. Studies of risk factors for varicose veins have largely resulted in inconsistent results; the sex difference is universal while the large geographical differences suggest strong environmental influ ences. For all other determinants much of the variation between studies is probably related to differences in definition, in population-sampling techniques, and in assess ment methods. Several plausible etiologic theories on the causes and development of chronic venous insufficiency are supported or refuted by the epidemiologic studies. Further research is needed, whenever possible cross-cultural, with particular emphasis on clear definitions, valid methods, and a prospective study design.