The demilitarization of ammunition that has reached the end of life (or become obsolete) has to be carried out with minimum energy and environmental impacts. The Portuguese Armed Forces have significant amounts of ammunition that need to be eliminated. In order to assess and improve ammunition demilitarization, a life-cycle approach must be adopted. The main goal of this article is to present a comprehensive life-cycle assessment (LCA) of the ammunition demilitarization performed by the Portuguese company IDD (Industria de Desmilitarização e Defesa). A life-cycle model was developed for the entire demilitarization process, which involves ammunition dismantling, discharging, the incineration of energetic material, and the subsequent flue gas treatment. A detailed inventory was based on data collected from the IDD. A life-cycle impact assessment was carried out, based on three complementary methods used to assess a total of ten impact categories: cumulative energy demand (primary energy); CML 2001 (six environmental impact categories) and USEtox (three toxicological categories). The results show that the main contributor in nine out of the ten impact categories is the incineration and gas treatment process, due to the high energy requirements (electricity and propane). Nevertheless, equipment manufacture also has a significant impact in the Human Toxicity (non-cancer) category, mainly related to the manufacture of the static kiln. These findings enhance our understanding of demilitarization using a static kiln, showing that the associated impacts are significant and should be reduced.