This paper summarizes fish collections taken from 1955 to 1969 in the vicinity of Tortuguero, Costa Rica. Most collections were made in the estuary during the summer rainy season, others in the tributary streams, ocean beach, and open ocean. The 111 species represented nearly double the total reported by Caldwell, Ogren, and Giovannoli (1959). Nine are additions to Miller's (1966) checklist of Central American freshwater fishes, and one species is described as new. Of the 80 freshwater species collected, six (7.5%) are primary division, 18 (22.5%) secondary division, and the remainder peripheral division forms, according to Myers' (1938) classification of freshwater fishes based on degree of salt tolerance. A list of collection localities is included, with pertinent ecological data, together with an annotated list of species and a summary table. The paper also summarizes previous literature pertaining to Central American freshwater and Caribbean shore fishes, discusses the zoogeographic relationships of the Tortuguero fish fauna, describes the geographical and ecological characteristics of the Tortuguero area, and discusses the assemblage of larval fishes and invertebrates (tismiche) periodically observed in the estuary.