4-oxo-flavonoids are dietary compounds widely distributed in the plant kingdom. Interest in these substances has arisen because of possible effects on human health. Indeed, in spite of extensive metabolism by the intestinal flora, 4-oxo-flavonoids seem to be sufficiently absorbed to have physiological effects. This review discusses the possibilities of a positive role in cardiovascular disease and cancer prevention, particularly by their antioxidant properties and their ability to modulate the activity of many enzymes, and summarizes the data concerning an eventual carcinogenicity of 4-oxo-flavonoids.