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Abstract.  The monotypic new family Ocoidae is described to accommodate Ocoa gen.n., small, elongate, delicate, asiloid flies known from west-central Chile, South America. Both sexes of adult O. chilensis sp.n. are described and illustrated; immature stages are unknown. Diagnostic morphological features of adults include the antennal postpedicel comprising a single, undivided structure consisting of a bulbous base and a long, threadlike terminal element; vein M3 lacking, anal vein complete; acropod heterodactylus; spurs lacking on all tibiae; and anterior surface of hind coxa with strong, knoblike, bulbous projection; and abdominal tergite 2 lacking sensory patches of hairs. The epandrium of the male terminalia is divided along the midline into two sicklelike sections; gonostyli articulate in a horizontal plane. The female terminalia has well-developed acanthophorite spines; posterior margin of hypoproct with several ventrally projecting, elongate, needlelike setae; two large, poorly sclerotized spermathecae; and a spermathecal sac that is smaller than each spermatheca. The relationships of this enigmatic family are discussed in relation to recent findings on the phylogeny and classification of the Asiloidea. Ocoidae are similar to Therevidae and close relatives Scenopinidae and Apsilocephalidae, comprising the therevoid group of families; however, they lack defining synapomorphies of those families. Morphological evidence supports a sister-group relationship between Ocoidae and Scenopinidae. Molecular evidence from 28S rDNA provides further support for the monophyly of the therevoid group of families, and suggests that Ocoidae belongs within this clade, in agreement with the morphological data. The nucleotide data place Ocoidae as sister to the Scenopinidae + Therevidae, but the morphology-based hypothesis of relationships (Ocoidae + Scenopinidae) is only two additional steps (0.2%) on the optimal trees from the molecular data.