Rhizocephalan barnacles of the genus Lernaeodiscus Müller, 1862, are uncommon external parasites of galatheid and porcellanid crabs, and most species are poorly known. Based on a thorough review of the literature and examination of new material, we summarize taxonomic and biogeographic knowledge about this genus. We report significant geographic range extensions and new hosts and correct or complete several identifications of both hosts and parasites previously reported in the literature. We present evidence that L. crenatus Boschma, 1969, is synonymous with L. porcellanae Müller, 1862, and that Atlantic and Pacific specimens of L. porcellanae are probably different species. Lernaeodiscus tableta n. sp. is described from specimens parasitizing the porcellanid Aliaporcellana suluensis from Indonesia.