This paper presents the first part of a study of large collections of Hydroida (Cnidaria : Hydrozoa) in the Museum national d'Histoire naturelle, Paris, originating from various expeditions in the Philippines, the eastern part of the Malay Archipelago, the Chesterfield Islands, New Caledonia and the Loyalty Islands. In this first part, genera of the family Sertulariidae Lamouroux, 1812, are reviewed, including new species of the genera Abietinaria Kirchenpauer, 1884 (1 new species), Dictyocladium Allman, 1888 (1 new species), Gonaxia nov. gen. (20 new species and a new variety), Sertularella Gray, 1848 (8 new species and a new subspecies), Symplectoscyphus Marktanner-Turneretscher, 1890 (6 new species and a new subspecies), and Thyroscyphus Allman, 1877 (1 new species). In addition to other, already known species from those genera, species of Caminothujaria Von Campenhausen, 1896, Cnidoscyphus Splettstosser, 1929, Dynamena Lamouroux, 1812, Geminella Billard, 1925, Hydrallmania Hincks, 1868, and Idiellana Cotton & Godfrey, 1942, are recorded. Many of the records are considerable range extensions or constitute new records for the Chesterfield Islands, New Caledonia and Loyalty Islands regions. Additional species and genera will be treated in a second part. Noteworthy is the occurrence of the curious new genus Gonaxia with many new species from the New Caledonia area, producing its gonothecae in intimate contact with the axis and its secondary tubules. Remarkable also is the occurrence of two northern Atlantic shallow water hydroids, Hydrallmania falcata (Linnaeus, 1758) and Diphasia attenuata (Hincks, 1861), the latter to be fully described in the sequel to this report, from deep water of the New Caledonia region. In zoogeographic context, the present study reveals a considerable degree of endemism in the deeper water hydroid fauna of the seas bordering New Caledonia and the Loyalty Islands, a phenomenon also observed amongst other groups of marine animals. Further zoogeographic comments will be postponed until a larger part of this highly interesting collection has been fully studied.