Coevolution of parasites and in particular monogeneans and fishes, was characterized from two related angles--parallel coevolution and host switches, lead to the acquisition of new hosts from taxonomically distant but ecologically similar groups. Modern views on the evolution and taxonomy of gudgeons are discussed. This group is very heterogeneous by morphology and biology, tales unclear taxonomic position in the family Cyprynidae, and can be divided into two tribes or four groups of genera. Analysis of coevolution of dactylogirids, ancyrocephalids, gyrodactylids, and diplozoids with their hosts was carried out. Dactylogyrus spp. and gudgeons show coevolutional connections; in Ancyrocephalus s. l. spp. coevolution and host switches take place; most of Gyrodactylus spp. parasitize fishes of the genus Gobio and are the colonists of gudgeons; and none of the diplozoids parasitize exceptionally gudgeons. From 130 species of 30 genera of the World fauna of gudgeons 31 species 13 genera proved to be infected with monogeneans. We divided the dactylogyrids from gudgeons (49 species) into 13 evolution levels and 30 morphological groups, which were found equal in number with taxonomic groups of hosts. Ancyrocephalids were divided into two evolution levels, which can not be reduced to one initial type, and eight monophyletic groups. Fourteen of 18 species of these monogeneans occurred on the host from the genera Hemibarbus and Squalidus. Different directions of evolution connected with forming of different types of copulatory organ, ventral additional bar, and type of attachment on gills were revealed for Dactylogyrus spp. from different groups of genera of gudgeons (Yang et al., 2006). Monogeneans have lower evolutionary rates, as compared with their hosts, that are expressed in the taxonomic ranks (groups of species in monogeneans and genera or groups of genera in their hosts). Number of species in Dactylogyrus and Ancyrocephalus s. l. usually the same as the number of their host species. However this proportion increases in favor of the parasites owing to the explosion-like speciation of monogeneans parasitizing Hemibarbus and Saurogobio. Distribution of morphological groups of monogeneans on gudgeons in general confirms their grouping into four groups of genera on the base of molecular data. At the same time, in some cases parasitological data agree with the gudgeons' classification based on morphological characters to a greater extent (Banarescu, 1992; Naseca, 1998). The genera Sarcocheilichthys and Gnathopogon take the crucial position in the Sarcocheilichthys group of genera according to the analysis of occurrence of monophyletic groups of Dactylogyrus spp. In the Pseudogobio group of genera, the largest number of the Dactylogyrus spp. groups was found on the genera Saurogobio and Abbottina. The genus Hemibarbus, being the host of some original groups of Dactylogyrus spp. and Ancyrocephalus spp., takes the most isolated position among gudgeons by morphological, molecular, and parasitological data. Relationships of Hemibarbus and Squalidus (both from the Hemibarbus group of genera) are need in further investigations. The Sarcocheilichthys group of genera, which contains the genera Coreius and Paracanthobrama with unclear and ambiguous positions, is situated apart from the Hemibarbus group of genera. High-specialized groups of Dactylogyrus spp. are predominating on the former. The Pseudogobio group of genera is parasitized by numerous primitive groups of Dactylogyrus spp. Groups of Dactylogyrus spp. from the Gobio group of genera are derived undoubtedly from the monogeneans parasitizing the Pseudogobio group of genera, and the Gobio group of genera either derived from the Pseudogobio group of genera or must be included into the latter. Thus, we have one phylum of gudgeons with separate groups of monogeneans (Hemibarbus group of genera) and, contrariwise, other phylum of fish hosts with ancient and specialized monogeneans (Sarcocheilichthys group of genera), which ends in the gudgeons with primitive monogeneans (Pseudogobio group of genera) and evolutionary young monogeneans (Gobio group of genera). The pattern of distribution of the morphological groups of monogeneans by gudgeons is a mirror reflection of modern contradictory views on the taxonomy and evolution of these fishes and may contribute to a more profound understanding of the place of gudgeons in Cyprinidae, their taxonomy and evolution.