A new biodiversity inventory of opomyzoid families (excl. Agromyzidae) in the Gemer area (Slovakia) is presented with a critical synopsis of previously published data and new records obtained from the Muránska planina National Park and the Cerová vrchovina Protected Landscape Area. The study includes the families Clusiidae (10 species), Acartophthalmidae (2), Opomyzidae (12), Anthomyzidae (14), Aulacigastridae (3), Stenomicridae (2), Periscelididae (5), Asteiidae (7) and Odiniidae (8). For each recorded species remarks on general distribution, biology, faunistic and/or nature conservation importance are provided. Four species, viz. Aulacigaster falcata Papp, 1998 (Aulacigastridae), Periscelis (Myodris) haennii Pollini Paltrinieri & Roháček, 2022 (Periscelididae), Neoalticomerus fabricius Withers & Papp, 2012 and Odinia photophila Papp, 1977 (second known specimen) (both Odiniidae), are recorded from Slovakia for the first time, and 14 other species are new additions to the fauna of the Gemer area, viz. Geomyza acutipennis Czerny, 1928, G. balachowskyi Mesnil, 1934, G. breviseta Czerny, 1928 and G. subnigra Drake, 1992 (Opomyzidae), Anagnota bicolor (Meigen, 1838), Anthomyza collini Andersson, 1976 and Stiphrosoma cingulatum (Haliday, 1855) (Anthomyzidae), Periscelis (Periscelis) annulipes Loew, 1858 (Periscelididae), Asteia elegantula Zetterstedt, 1847 and Leiomyza birkheadi Gibbs, 2007 (Asteiidae), Neoalticomerus formosus (Loew, 1844), Odinia czernyi Collin, 1952, O. meijerei Collin, 1952 and O. trinotata Robineau-Desvoidy, 1830 (Odiniidae). First records of Neoalticomerus fabricius are also given from Germany, Poland and Czech Republic. Except for the above new faunal records, also the following species are considered interesting and important in the Gemer area because of their rarity or significance from the nature conservation point of view: Clusiodes gentilis (Collin, 1912) (Clusiidae), Stiphrosoma humerale Roháček & Barber, 2005 (Anthomyzidae), Podocera soniae (Merz & Roháček, 2005) (Stenomicridae), Periscelis (P.) laszloi Roháček, 2022 and P. (P.) winnertzii Egger, 1862 (Periscelididae). Diagnostic characters of some species of Odiniidae are emphasized and illustrated.
