In order to update and summarize the information about the diversity of the medusozoans occurring in Mexican waters, records were reviewed at the family level to assess the current status of the knowledge of the diversity of this group in Mexico. A synthesized revision of different biological and ecological aspects of the group is also presented. In addition, new records are included of: Crossota millsae, Halitrephes maasi, Atorella octogonos, Tiburonia granrojo, Stygiomedusa gigantea, Periphyllopsis braweri, Resomia persica, Bargmannia lata, Desmophyes haematogaster and Lensia quadriculata, found in the Gulf of California. The results of this analysis yielded a total of 289 species of Medusozoa known in Mexico, of which 3 species are of Cubozoa, 20 of Scyphozoa, and 266 of Hydrozoa. Overall, the number of species recorded in Mexican waters represents about 7.3% of the medusozoans known worldwide, thus suggesting that the diversity of the group deserves further efforts, particularly in scarcely surveyed habitats.