Gilles-Eric Seralini, et. al just published a study in Journal of Food and Chemical Toxicity purportedly showing that rats on a diet of Monsanto's Roundup-tolerant genetically engineered corn developed more tumors and died sooner than rats on a non-GMO diet. The 'purportedly' modifier is included in the previous sentence intentionally. It turns out that the data do not seem to actually support these conclusions--at least not the published results.
The study's publication and Seralini's subsequent press conference at the European Parliament a day later lead to a flurry of coverage from groups concerned about GMOs. It also precipitated serious criticism from a range of scientists who questioned the methods, gaps in the reported data, and the way the data was analyzed. Hank Campbell, on the Science 2.0 website, conveniently cataloged many of the specific concerns and comments from other scientists about the study.
Nevertheless, the report has prompted the French Prime Minister, Prime Minister Jean-Marc Ayrault to ask the European Food Safety Authority (EFSA) to look into the study. Also, promising that, if the results are confirmed, he would seek a European ban on GMOs. The EFSA may have difficulty confirming the results though since the lead author, Dr. Seralini, has reportedly refused to release the data to the agency. He has concerns that they are biased since they approved the corn previously.
University of Caen's researcher Dr. Gilles-Eric Seralini has been a longstanding critic of GMOs. He co-founded the Committee for Research and Independent Information on Genetic Engineering. The group describes itself on their English-version website as, "an independent non-profit organization of scientific counter-expertise to study GMOs, pesticides and impacts of pollutants on health and environment, and to develop non polluting [sic] alternatives."
For a detailed analysis of the study, take a look at Scicurious's critique on the Discover Magazine website. Also, it is worth it to check out Andrew Kniss' illuminating statistical analysis on the viability of the Sprague-Dawley rats used in the study. It seems that two year old rats develop tumors about 72% of the time.