The poorly known European species Janetiella thymi (Kieffer), type species of Janetiella Kieffer (Diptera: Cecidomyiidae), is redescribed. Gall makers on grape that were formerly placed in Janetiella are shown to be distinct from that genus and transferred to Vitisiella Fedotova & Kovalev, a genus recently erected for a species on grape in Siberia. Among the distinguishing traits of Vitisiella, more fully characterized here than previously, are the closed costal vein at its juncture with R₅, the deeply divided male hypoproct, and the conspicuous dorsolateral sclerites of the ovipositor. Janetiella brevicauda Felt, also redescribed, and Cecidomyia oenephila Haimhoffen, both previously placed in Janetiella, are newly combined with Vitisiella.