RESUMEN
This paper describes a dataset of polychaetes (Annelida) from 14 midlittoral rocky shore sampling sites in Greece and Italy (Mediterranean Sea). The dataset combines the outcome of four different projects studying the hard substrate midlittoral zone in the Mediterranean between 1984 and 2009. Samples were collected by scraping and collecting the organisms from a framed area. The maximal sampling depth was 1.5 m. In total, 123 polychaete species were recorded, five of which are new records for the respective biogeographic sectors of the Mediterranean. The dataset contains 788 occurrence records, fully annotated with all required metadata. These data contribute to the knowledge of a previously very understudied regional habitat, since at present, comprehensive lists of the midlittoral communities in the Mediterranean are provided through only a few, paper-based, studies. This dataset is one of the first electronic data compilations of the Mediterranean midlittoral zone communities and certainly the most comprehensive of its kind, contributing to the ongoing efforts of the Ocean Biogeographic Information System (OBIS) which aims at filling the gaps in our current knowledge of the world's oceans. It is accessible at http://ipt.vliz.be/resource.do?r=mediterraneanpolychaetaintertidal.