At least four different species of the toxic dinoflagellates cause shellfish and fish poisoning in the United States: Ptychodiscus brevis, neurotoxic shellfish poisoning; Protogonyaulax catenella and P tamarensis, paralytic shellfish poisoning; and Gambierdiscus toxicus, ciguatera fish poisoning. These three disorders have similar clinical manifestations, primarily neurologic and alimentary. A complete history is essential; confirmation, while dependent on specific laboratory analysis, is usually based on a history of ingestion of fish or shellfish previously associated with these types of poisonings. The principal toxins affect sodium channels; Ptychodiscus brevis toxins and ciguatoxin by stimulating these channels and saxitoxin by blocking them. Since no antidote is known, treatment is symptomatic. Public health measures and public education are necessary to prevent this form of poisoning.