Samples from 5 Danish freshwater trout farms rearing rainbow trout (Oncorhynchus mykiss) were examined for parasite infections from October 1993 until November 1994 and recorded parasites are listed. In addition, results from an examination of a mariculture net cage system are presented as well. A total of 10 metazoan and 10 protozoan parasites were recorded. The metazoans included Gyrodactylus derjavini, Gyrodactylus salaris, Eubothrium crassum, Triaenophorus nodulosus, Proteocephalus sp., Diplostomum spathaceum, Tylodelphus clavata and Argulus foliaceus from the freshwater farms. The protozoans Hexamita salmonis, Ichthyobodo necator, Ichthyophthirius multifiliis, Apiosoma sp., Epistylis sp., Trichodina nigra, T. mutabilis, T. fultoni, Trichodinella epizootica, and an Ichthyophonus like intestinal parasite were also detected in the freshwater trout farms. Based on lectin binding studies, few fish were found positive for the myxosporean parasite PKX although no clinical cases were reported. In the mariculture system, Lepeophtheirus salmonis and Caligus elongatus were found.