The composition, richness and similarity of helminth communities in a tropical freshwater fish were determined in samples of Cichlasoma urophthalmus collected from 7 localities of broadly similar age and character situated along the northern coast of the Yucatan peninsula, Mexico. The component communities exhibited a unique combination of characteristics for a freshwater fish. They were dominated by digeneans, with all other helminth groups being numerically inferior. A common suite of species could be recognized, but many of its members were generalists and not cichlid specialists. Species richness and number of individuals per host were high, but diversity was low, reflecting high dominance by one species. Intra- and inter-locality similarity levels were low, and local variation high. In respect of species richness and digenean dominance, the communities resembled those in Australian tropical anguillids, but in respect of low diversity, similarity and high dominance they are more similar to helminth communities of northern temperate fish.