For Pacific lampreys, life is not just about moving from freshwater to saltwater when they reach maturity, these ancient fish have to return to the same river environment where they were born. Going from a saltwater creature to a freshwater creature is not easy, however, and several modifications in appearance and physiology are necessary to survive the dramatic change in salinity. Their return to freshwater is not random, based on chemical signals left by the migration of lamprey larvae to return to rivers They can return to the same place they came from, but, unlike Pacific salmon, this precision is not always guaranteed, however, this transformation and the mapping of rivers require a lot of energy, and the animals resort to parasitization to survive. Lamprey swimming is among the most efficient in the world, as its movements generate zones of low pressure around the body, pulling the body through the water rather than pushing. The objective of this article was to characterize lampreys (Cyclostomata; Petromyzontiformes; Petromyzontidae) regarding their ecological and medicinal importance. The methodological analysis included studies of a particular topic. In its construction process, it is necessary to go through six essential stages: Identification of the theme and selection of the hypothesis or research question; establishment of criteria for inclusion and exclusion of studies/sampling or literature search; definition information to be extracted from selected studies/categorization of studies; evaluation of included studies; interpretation of results; and presentation of knowledge review/synthesis To carry out the study, a search for scientific articles was carried out through Virtual Health Library, in the SCIELO, LILACS, and PUMED databases, using the terminologies registered in the Health Sciences descriptors. Regarding the inclusion criteria, the following were used: Full articles, in Portuguese, and English.