The first catalogue including al1 the hydrozoan species from the Iberian Peninsula, Balearic Islands and the neighbouring Alboran Island has been made. Species distribution are catalogued following political regions along the Iberian coasts. Zoogeographical affinities are shown at various levels. The significance of the dispersive stage of the hydrozoan life cycle is considered. Affinities of the hydrozoans species in the different regions are also discussed.