In 2009 and 2010, the EFSA GMO Panel concluded the assessment of genetically modified (GM) maizes MIR604, MIR604 × GA21, MIR604 × Bt11 and MIR604 × GA21 × Bt11. These maizes were found to be as safe as their conventional counterparts and other appropriate comparators with respect to potential effects on human and animal health and the environment. On 23 July 2015, the European Commission (EC) received from Syngenta new nucleic acid sequencing data on maize event MIR604 and updated bioinformatic analyses using the new sequencing data. EC tasked EFSA to analyse these data and to indicate whether the previous conclusions of the EFSA GMO Panel on the above-listed GM maizes remain valid. The EFSA GMO Panel used the appropriate principles described in its guidelines for the risk assessment of GM plants to analyse the received data. The new sequencing data indicated a single base pair difference compared to the sequencing data originally provided, located in a non-coding region of the insert. which had already been present in the original plant material used for the risk assessment. Thus, with the exception of bioinformatics analyses, the studies performed for the risk assessment remain valid. The new sequencing data and the bioinformatic analyses performed on the new sequence did not give rise to safety issues. Therefore, the GMO Panel concludes that the original risk assessment of event MIR604 as a single and as a part of stacked events remains valid.