Ribesia sarae Gagné, new genus, new species (Diptera: Cecidomyiidae), is described from simple leaf blister galls on Ribes aureum (Grossulariaceae) from Montana, USA. The female abdomen of Ribesia is superficially similar to that of Cystiphora Kieffer and Sackenomyia Felt. The three genera are compared. Because of strong differences found in their male terminalia it appears that any similarities in the female abdomens are the result of convergence. Sackenomyia ribesifolia Fedotova 1987 from Ribes in Kazakhstan is a new combination in Ribesia.