A comparative description of imagines, subimagines, and nymphs of Cloeon dipterum (L.) s.r., C. cognatum Stephens stat. nov., and C. inscriptum Bengtsson stat. nov. is given on the basis of reared material from southern Poland. The recognized and probable synonyms of these species are discussed on the basis of the data from European literature. Remarks about the material from other parts of Europe and about the type specimens of the three species are also given.