White maize in South Africa is the only staple crop produced on a widespread commercial basis for direct human consumption using genetically modified (GM) cultivars. Using a combined economic and environmental approach, we estimate the total welfare benefits attributable to GM white maize in South Africa for 2001-2018 are 694.7million.FoodsecuritybenefitsattributabletoGMwhitemaizeinSouthAfricaalsomanifestthroughanaverageof4.6millionadditionalwhitemaizerationsannually.Toachievetheseadditionalannualrationsusingconventionalhybridmaize,theadditionallandrequiredwouldrangefrom1,088hectaresin2001to217,788hectaresin2014.ResultsindicatethatGMmaizereducesenvironmentaldamageby0.34 per hectare or $291,721 annually, compared to conventional hybrid white maize