The collections made by the Smithsonian Tropical Research Institute's Environmental Protection Agency supported oil pollution study, the National Museum of Natural History Panama Survey, and other collections from Middle America contain 64 species of Pycnogonida, including 17 previously undescribed species. Twenty-eight species are discussed from Pacific localities and 35 species from the Caribbean. Sixteen species are now known to be found on both shores of Middle America. Previous literature on Middle American pycnogonids is reviewed and a resumé of faunal affinities is given for both oceans. It is proposed that there is no endemic pycnogonid fauna on either the Caribbean or Pacific coasts of Middle America. Diagnostic keys, references, and distribution records are provided for all shallow-water pycnogonids of this region.