The hydroids belonging to the genus SertularellaGray, 1848 from southern South America and the subantarctic are revised, based on both literature data and the reexamination of type specimens and additional material dealt with in earlier accounts. Thirty-two species are recognized as valid, of which five are new to science, namely S. juanfernandezensis, S. oblonga, S. recta, S. robustissima, and S. subantarctica. Modern redescriptions of S. implexa (Allman, 1888) and S. novaraeMarktanner-Turneretscher, 1890 are provided. Additionally, it is demonstrated that S. argentinicaEl Beshbeeshy, 2011 and S. jorgensisEl Beshbeeshy, 2011 are junior synonyms of S. clausa (Allman, 1888) and S. valdiviae Stechow, 1923, respectively. Sertularella paessleriHartlaub, 1901 is assigned to the synonymy of S. allmaniHartlaub, 1901, S. lagenaAllman, 1876 to that of S. contortaKirchenpauer, 1884, S. picta (Meyen, 1834), S. protectaHartlaub, 1901 and S. margaritaceaAllman, 1885 to that of S. gaudichaudi (Lamouroux, 1824), Sertularella uruguayensis Mañé Garzón & Milstein, 1973 to that of S. mediterraneaHartlaub, 1901, and S. striata Stechow, 1923 to that of S. patagonica (d'Orbigny, 1842). Lectotypes are designated for S. allmani, S. antarcticaHartlaub, 1901, and S. implexa. A checklist of all species records from the study area, together with new identifications, is provided as an appendix.