Taxonomy, morphology and geopgraphical distribution of 5 species of Hydraenidae(Hydraena ripariaKugelann,H. assimilisRey,H. melasDalla Torre,H. reyiKuwert andH. egoniJäch), belonging to theHydraena ripariacomplex are discussed. New synonymies, greatly affecting the nomenclature within the complex, are established:Hydraena melas (= bohemica Hrbacek=sternalisRey) andreyi (= sternalissensu auctorum, not Rey).Hydraena assimilisregarded until today as a synonym of Hripariais shown to be a species propria, distinguished fromH. ripariaby its considerably shorter aedeagal flagellum. Neotypes are designated forH. riparia, H. melas, H. laevisDalla Torre andT. brunneaDalla Torre. Lectotypes are designated forH. longipalpisMarsham,H. signataRey,H. bipunctataRey,H. cribricollisRey andH. reyi.Morphological details of the last abdominal segments of the females were thoroughly studied to permit their identification. Distribution maps are provided for all five species.