In this opinion, the GMO Panel assessed the four-event stack maize Btll x MIR162 x 1507 x GA21 and three of its subcombinations, independently of their origin. The GMO Panel previously assessed the four single events and seven of their combinations and did not identify safety concerns. No new data on the single events or the seven subcombinations leading to modification of the original conclusions were identified. Based on the molecular, agronomic, phenotypic and compositional characteristics, the combination of the single events in the four-event stack maize did not give rise to food/feed safety issues. Based on the nutritional assessment of the compositional characteristics of maize Btll x MIR162 x 1507 x GA21, foods and feeds derived from the genetically modified (GM) maize are expected to have the same nutritional impact as those derived from non-GM maize varieties. In the case of accidental release of viable grains of maize Btll x MIR162 x 1507 x GA21 into the environment, this would not raise environmental safety concerns. The GMO Panel concludes that maize Btll x MIR162 x 1507 x GA21 is nutritionally equivalent to and as safe as its non-GM comparator in the context of the scope of this application. For the three subcombinations included in the scope, for which no experimental data were provided, the GMO Panel assessed the likelihood of interactions among the single events and concluded that their combinations would not raise safety concerns. These maize subcombinations are therefore expected to be as safe as the single events, the previously assessed subcombinations and the four-event stack maize. The post-market environmental monitoring plan and reporting intervals are in line with the intended uses of maize Btll x MIR162 x 1507 x GA21 and its subcombinations. A minority opinion expressed by a GMO Panel member is appended to this opinion. (C) 2018 European Food Safety Authority. EFSA Journal published by John Wiley and Sons Ltd on behalf of European Food Safety Authority.Read less <