Descriptions of the chromosome complements of one species of the Richardiidae, ten of the Otitidae and nine of the Platystomatidae, are added in this report to the two for Otitidae provided by Metz (1916). The 2n = 10 complement of the single Richardiidae species had a total complement length (TCL) of 68.7μ. Complements of the 12 Otitidae species ranged from 2n = 6 to 12 and averaged 45.8μ in TCL whereas those of nine Platysiomatidae ranged from 2n = 6 to 12 and averaged 41.4μ in TCL. Morphological differences between complements having the same chromosome number are discussed. A karyotype having a short telocentric sex pair and five meta-to submetacentric autosomal pairs constitutes a common karyological feature and could be the basic (primitive) karyotype of species of Acalyptrate and Calyptrate Diptera. It is suggested that the basic 2n = 12 complements of Drosophila species (10 rods and 2 dots) may be far from typical for species of such Diptera.