Vegetables are the major source of dietary nitrate, with wide variations in nitrate content. The presence of nitrate in vegetables is often associated with harmful effects on human health, i.e. with toxic effects of methaemoglobinaemia and the possibility of causing an endogenous formation of carcinogenic N-nitroso compounds. However, it is also associated with beneficial health effects, since nitrate represent an important alternative pathway to bioactive NO and its important physiological roles in vascular and immune function. In this review the concentrations of nitrate in different vegetables from different countries are given. Furthermore, the reasons for the different contents of nitrate in vegetables, the daily intakes and comparisons to the acceptable daily intake (ADI) values, legislation, metabolism and toxicology of nitrate are described as well as harmful and beneficial effects of nitrate on human health.