This paper contains a historical review of literature pertaining to the external morphology of the family Sphaeroceridae and related acalyptrate Diptera, and a detailed account of adult morphology of Sphaerocera curvipes Latreille, with which other species in the same genus as well as in other genera are compared. This study has 3 objectives: (1) to define the terms used by taxonomists for certain structures morphologically and to synonymize the non-morphological terms that have appeared in the literature; (2) to attempt to trace, insofar as possible, the homologies of various structures in the family Sphaeroceridae with those of other Diptera; and (3) to point out the most important modifications within the group preliminary to the study of the phylogeny of the family. An extensive account of the organization and the lateroversion of the male postabdomen and genitalia is also presented with the discussion of theories on the lateroversion of the male postabdomen of Diptera. This study was made to establish a sounder basis for the systematics of the family.