Companies have established ISO 14001 Environmental Management System for some reasons. These reasons, which contribute to decide for implementing, are attractive returns of ISO 14001 Environmental Management System. However, ISO 14001 Environmental Management System has brought some problems and shortcomings for the companies implementing it. Aim for this thesis to investigate and discuss what the most critical problems, shortcomings and featured benefits are in implementation period of ISO 14001 EMS for companies. In addition to all, another goal of this study is to identify the differences between companies depending on sector and locations of facilities (in Istanbul and out of Istanbul) in terms of problems and benefits. Two main hypotheses of this study are that; First is; "There are differences between the types of facilities in terms of problems, shortcomings and benefits of ISO 14001 EMS." Second is; "there are differences between the locations of organizations in terms of problems and benefits of ISO 14001 EMS."