This article analyzes the long-term feeding study of Séralini et al.,1 in which rats were fed for over two years with genetically modified maize NK 603 treated with and without Roundup Ready and drinking water containing Roundup. In the study the rats died earlier and developed more tumors than rats from a control group. However, these findings are questionable because there are serious methodical flaws and shortcomings in the representation of the data, and the published data do not allow an interpretation of increased cancer rates and premature death. Due to the low number of animals used in the test groups, it appears that these observed effects occurred by chance. The consequences of the study are discussed in respect of risk assessment of genetically modified organisms and the authorization process.