The environmental performance evaluation (EPE) of organizations is becoming an autonomous management tool. The main goal of this research was to assess the state of EPE practice in the Portuguese defence sector, as a particular part of public services. A questionnaire survey was conducted involving all Portuguese military units that have a person in charge of environmental issues. The questionnaire was designed to assess: (i) the importance and drivers of EPE; (ii) the ISO 14031 knowledge and implementation; (iii) the knowledge and use of environmental indicators; (iv) the optimal format for indicators; and (v) the advantages and drawbacks of using environmental indicators. Despite various initiatives driving environmental practices in public organizations, most of that experience is only centred on an environmental management system, and EPE is quite a new issue. Nevertheless, general environmental performance evaluation is a growing reality and one in which Portuguese military units are taking an increasing interest. Overall respondents agree on the importance of measuring and communicating environmental performance related to their main missions and activities. The main drivers for EPE in military units are the prevention of health risks and compliance with regulations. However, to date, ISO 14031 and environmental performance indicators are almost unknown in the respondent military units. Among the three military branches, the Navy revealed the worst environmental performance evaluation knowledge, awareness and practice.