The first genetically modified (GM) maize hybrids were registered in the Commercial Variety Register in Spain on 26 March 1998. The registered hybrids, Compa CB and Jordi CB, were carrying the genetic modification identified as event 'Bt-176'. This genetic modification expresses the Cry1Ab protein from Bacillus thuringiensis for protection against the insect pests: European Corn Borer Ostrinia nubilalis and the Mediterranean Corn Borer Sesamia nonagrioides. Since then and until 2005, Spanish farmers have planted Bt-176 maize on their farms, growing to well over 22,000 hectares annually (5% of total acreage). As part of the Spanish hybrid registration, the Spanish Authorities required that a post-market monitoring plan be implemented, which addressed several points. Syngenta presented a monitoring plan which was further developed and carried out in collaboration with public research institutions in Spain. The monitoring plan has been in effect and results are now available. The results support the initial conclusions from the regulatory safety assessments, which were that Bt-176 maize is as safe as its conventionally bred counterpart, and indicate that Bt-176 maize does not have any unexpected negative impacts to the environment in Spain. The results of the post-market monitoring plan and our commitment to stewardship for Bt-176 maize in Spain are reviewed in more detail, and we describe how these studies reinforce the conclusions from the initial regulatory assessments.