Bahía Fosforescente, Puerto Rico, is well-known because of biolurniniscence caused by high concentrations of dinoflagellates. However, the specific cornposition of dinoflagellates has not been studied in detail. Several samples taken during 1975-1987 with net were analysed to study the dinoflagellates in the bayo Twenty-six taxa were identified, including 19 species, ti varieties, and one form, together with three species not fully identified, all of thern thecate. The valid, currentIy recognized names, as well as sorne synonyrns are given, together with references, illustmtions and distribution data. This study shows the constant presence of the species responsible for the bioluminiscence in the bay, Pyrodinium bahamense. The taxa Ceratium hircus and Dinophysis caudata varo ventricosa also occurred in all seasons. The genus Protoperidinium is represented by the greatest nurnber of species in the bay (15). The unique hydrogmphic characteristics. registered in the bay, such as the tidal and wind-driven mechanisms make possible the diversity of typically plankt()nic dinoflagellates in a shallow environrnent, although one benthic form was also found.