This study analyzes the sustainable efficiency of companies that are part of the Corporate Sustainability Index (ISE) and that publish their sustainability reports following the guidelines of the Global Reporting Initiative (GRI). In the quest to understand how sustainable organizations are, several indexes were developed, one of which is the ISE. This is a quantitative study, based on Data Envelopment Analysis (DEA), with the aid of the DEA-SAED software covering data for the year 2016, of thirteen companies that were present on the ISE list in the 2015-2017 period. The results indicate that four companies have achieved sustainable efficiency, two in the energy sector, one in the communications segment and one in cellulose/paper. It is concluded that the efficient companies, participating in the study, are heterogeneous, belonging to different sectors. It is also concluded that participating in the ISE and publishing its reports in the GRI format is no guarantee of achieving sustainable efficiency.