The sperm structure of some genera belonging to Cecidomyiidae dipterans is reported. Spermatozoa are immotile, as their axonemal doublets are devoid of dynein arms. Sperm cells ofContariniaand related genera (Allocontarinia, Lestodiplosis, Myricomya)arecharacterized by a flattened tail with the plasma membrane adapted to form orderly evaginations, each containing a microtubular doublet. The results do not support the inclusion of the genera among members of the subfamily Cecidomyiinae.Syndiplosis,retained to be a synonym ofContarinia,has a different sperm structure. The results are discussed in relation to the traditional taxonomy. A hypothetical evolution of the group based on the different sperm models till now described is also proposed.