Freshwater vertebrates from Mae Sa Stream, Doi Suthep-Pui National Park, Chiang Mai, were collected from January 1997 to June 1999. They comprised 3,900 fishes of 32 species; 149 amphibians of 9 species; and 3 reptiles of 3 species. Fifty-six species of helminths were recovered: the 5 monogenea were Dactylogyrus sp I, Trianchoratus sp, Gyrodactylus sp, Diplozoon sp and Dactylogyrus sp II; the 27 trematodes were Allocreadium sp I, II, Haplorchoides sp (metacercaria; meta), Posthodiplostomum sp, Gauhatiana sp, Plagiophorus sp, Transversotrema patialense, Euryhelmis sp, (meta), Centrocestus caninus (meta), Acanthostomum sp (meta), Genarchopsis goppo, Phyllodistomum sp I, Brevicreadium sp, Gorgoderina gracilis n sp, Pleurogenoides sphaericus, Stellantchasmus falcatus (meta), Haplorchis sp (meta), Urotrema sp, Haplorchoides sp (adult), Encyclometra bungara, Pleurogenes chiangmaiensis, Telorchis sp, Mantereilla sp, Genarchopsis sp (meta), Phyllodistomum sp II, Phyllodistomum sp III, and Ganeo tigrinus; the 6 species of cestodes were Senga chiangmaiensis n sp, Ptychobothrium mystacoleucusi n sp, P. rojanapaibuli n sp, P. discusae n sp, Circumoncobothrium baimaii n sp and Ptychobothrium maesae n sp; the 3 species of acanthocephala were cystacanth, Pallisentis sp, and Acanthocephalus lucidus; the 15 species of nematodes were Spinitectus sp (cyst), Rhabdochona sp, Rhabdochona sp I, Camallanus sp, Zanclophorus sp, Spinitectus sp (adult), Anisakis sp, Unknown I, II, Rhabdochona sp II, III, Proleptus sp, Cosmocerca sp, Ascaridia sp, and Camallanus anabantis. Specimens were surveyed one of each season for the first year. The prevalence (%) and intensity of infection were recorded. The second year and half of the third year, they were collected every two months. Parasite distribution, relationships between host and parasite, and classification, were analyzed by cluster analysis.