Macquarie Island (54°37'S 158°54'E) has been investigated for the occurrence of freshwater macroturbellarians. Twenty sites were examined but only one species, here ascribed to the genus Minona sensu lato of the Monocelididae, was found and it is described as Minona amnica sp. nov. Its closest taxonomic relationships seem to be with M. istanbulensis Ax from the Black Sea, and M. mica Marcus from Brasil. The new species is unusual in that it occurs throughout the fresh waters of the island even though it is a member of a predominantly marine group. Minona amnica occurs from windswept plateau lakes down to brackish water near the sea and data concerning the distribution and relative abundance of the species in various habitats are presented and discussed.