The brown algaSargassumprovides a natural substrate occupied by hydrozoans in shallow marine waters. A global count in 2007 listed 39 epibiotic species of Hydrozoa growing onSargassum, but more studies have been published since, therefore, an update is timely, particularly due to the increased abundance ofSargassumin the Caribbean. This review, based on a recent literature survey and new records from Mexico, includes 133 publications of epibiotic hydrozoans onSargassumspanning 220 years, from 1802 to 2022. A total of 131 hydrozoan species were recorded on 26 species ofSargassum, most belonging to the subclass Hydroidolina (130), with only one record of a trachyline medusa (Gonionemus vertens, subclass Trachylinae). Most publications centered on the Tropical Atlantic, where the greatest number of hydrozoan species (67 species) were recorded. All hydrozoan species possess a hydrorhiza, except one hydromedusae species that attach toSargassumvia adhesive tentacles. Most of the hydrozoan species associated withSargassumexhibited a benthic life cycle (93 species) and are comprised of erect, branched colonies (67 species) and large hydrothecae (69 species). Although the number of studies of epibiotic hydrozoans onSargassumhas increased since the mid-20th century, nevertheless hydrozoan richness has not reached an asymptote. Therefore, more sampling ofSargassumspecies would likely identify more hydrozoan species associated withSargassum, especially among benthicSargassum, and might help reveal potential biogeographical and ecological patterns betweenSargassumand hydrozoan epibionts.