Isopods are a diverse peracarid crustacean group with marine, freshwater and terrestrial representatives. Isopod species lists were typically prepared according to different habitats, which was true also for Slovenia. Here, we prepared the first unified overview of isopod species for Slovenia, which is also the first list of marine isopods in the country. We examined scientific publications, research reports and institutional databases. A total of 126 species have been recorded in Slovenia, of which 31 are marine, 21 are found in freshwater, and 74 are terrestrial. Of these, we report on seven marine and one terrestrial species for the first time. A major part of freshwater isopod richness is linked to the subterranean environment, where most endemic species for the country can be found. Among marine species, many are parasites, with potential economic impact, and two species are considered introduced. When the new species list is considered with valid national legislation, only 41 species retained the same taxonomic status. Many synonyms and invalid taxa according to recent taxonomy point out the need for revision the national red list of Malacostraca as well as other nature protection acts.