The mycetophilid fly genus Leptomorphus Curtis is known from all biogeographic regions except Australasia and Antarctica, and currently contains 28 extant species placed in four subgenera. The centers of diversity for this genus are central Africa and northeastern North America. There are nine species, in two subgenera, recognized from the Nearctic region (one Holarctic), though the limits of these species have not been adequately determined, resulting in confusion about their distributional limits. This confusion has been furthered by the lack of work on Mycetophilidae systematics and ecology, leading to only occasional records for this genus. The limits of Nearctic Leptomorphus species are determined using morphological characters and the phylogenetic relationships of the species and subgenera discussed. The distributional range of each species is also given. The placement of Leptomorphus with respect to other genera in the tribe Sciophilini is discussed. Differences between groups of species assigned to Leptomorphus raise questions about the validity of previous synonymizations and the usefulness of the Leptomorphus subgenera.