Rainbow trout (Oncorhynchus mykiss) from three Turkish farms were sampled monthly from May 2003 to June 2004 to determine ectoparasite seasonality, prevalence, and intensity. Smears of gills, skin, and fins of 1260 larvae to market-size fish were examined. Six protozoans and one monogenean were found: Ichthyobodo necator, Chilodonella piscicola, Ichthyophthirius multifliis, Gyrodactylus sp., Trichodina claviformis, Apiosoma piscicolumn, and Hexamita salmonis. The first three were found mainly in fry and all except I. multifiliis occurred in low temperatures from late fall through early spring. Infections of C. piscicola and Gyrodactylus sp. were persistent and T. claviformis was found for the first time on rainbow trout in the area.