The spermatozoa of some species of Diptera belonging to the Psychodidae are described. In the 4 species examined, they appear needle-shaped, non-motile, anteriorly flattened, posteriorly bifid. Flagella, and any microtubule system, are lacking, and the only organelles encountered are an extremely elongated nucleus, a prominent acrosome, a well developed subacrosomal body, a slender, somewhat elongated mitochondrial derivative and a conspicuous multilayered membrane wall, produced by the superimposition of the plasma membrane and the acrosomal membrane. The mitochondrion is devoid of a crystalline axis, while the acrosome contains a longitudinal, cross-striated para-crystalline body. Centrioles are absent throughout the spermatid stage. Sperms and spermatids are organized in syncytia of 210 elements.