Four expeditions were made to Coiba National Park between 1996 and 1998 to characterize this part of the poorly known Panamian Pacific polychaete fauna. The samples were collected by SCUBA diving, either by removing 4 kg blocks of dead coral (Pocillopora sp.) or scraping off 25 x 25 cm quadrats of Telesto multiflora or algae (Dyctiota cf. flavellata, Padina cf. durvillaei and another currently unidentified species). This paper deals with the Syllinae from hard substrates. Twenty-two species belonging to six genera of the subfamily Syllinae Grube, 1850 (Syllidae: Polychaeta) are reported. A new species, Syllis castroviejoi, is described. Four species are newly reported for the Eastern Pacific: Syllis beneliahuae (Campoy & Alquézar, 1982), S. botosaneanui (Hartmann-Schröder, 1973), S. corallicola Verrill, 1900 and S. garciai (Campoy, 1982), and, likewise, two species are first reports for the Central American Pacific coast: Branchiosyllis pacifica Rioja, 1941 and Syllis truncata Haswell, 1920. Two species, Syllis magna (Westheide, 1974) and S. pigmentata (Chamberlin, 1919), are newly reported for Panama.