Macrolabis americana Dorchin n. sp. is a newly discovered species of inquilinous gall midge found in galls of Dasineura folliculi Felt on two goldenrod species, Solidago rugosa Miller and Solidago gigantea Aiton (Asteraceae) in central Pennsylvania. This is the first record of Macrolabis outside the Palaearctic, where the genus is represented by 58 species. Contrary to what is known of most Macrolabis species, the new species is multivoltine and is found in galls induced by successive generations of D. folliculi. Despite certain biological similarities to Macrolabis solidaginis Fedotova, which is associated with Dasineura galls on goldenrod in Kazakhstan, its relations to its Eurasian congeners are currently unknown. Adults, larvae, galls, and life history of the new species are described.