In 1999, there has been much concern on the safety of genetically modified (GM) foods, an important and complex area of safety research, which demands rigorous standards. Various groups, including consumers and environmental Non Governmental Organizations (NGO) have suggested that all GM foods should be subjected to long-term animal feeding studies before approval for human consumption. The main goal of this review has been to know which is the state-of-the art regarding to the potential adverse effects of GM foods. Two databases, MEDLINE and TOXLINE, as well as a number of URL from INTERNET were used for references. Although commentaries, general news and letters to the Editor have been frequently published in reputable journals, papers about experimental studies on the safety of GM foods are surprisingly very scant. If data on toxicological assessment of GM foods have been obtained, these have not been reported in scientific journals and subjected to the scientific judgement.