Skin morphology of Atlantic salmon, Salmo salar, parr infected with Gyrodactylus salaris was examined for 3 yr in the river Batnfjordselva in Norway and compared to that of uninfected salmon parr from a neighboring river. The epidermis of the infected population had more cell layers and was thicker than the epidermis of parr from the uninfected population. The number of mucous cells did not differ, and no seasonal changes in morphology of the epidermis were detected in either rivers. Intensity of G. salaris did not correlate to epidermal thickness, epidermal cell layers, or mucous cell concentration.