A feeding study was carried out for fourteen weeks to evaluate the effects of partial inclusion of 5, 10 and 15 % of dillisk, Palmaria palmata, into formulated Atlantic salmon (Salmo salar) diets. A further fourth diet was produced without the presence of algae and was used as a basal reference diet. All the four diets were formulated to be iso-nitrogenous (40 %), iso-lipidic (25 %) and iso-energetic (26 MJ kg(-1)). Salmon growth (final body weight, weight gain, feed conversion ratio (FCR), specific growth rate (SGR)) were comparable across algal and control diets, with no significant differences amongst the treatments (P > 0.05). Comparisons of liver weight, viscera weight and viscerosomatic index (VSI) also suggested that the macroalgal inclusion did not affect fish growth (P > 0.05). Fish health indicators across haematological, immunological and hepatic function were generally similar between the experimental diets. The exceptions to this pattern included a significant decrease in alanine transaminase activity (P < 0.05) in the diet with 5 and 15 % P. palmata inclusion compared to other experimental diets. This may indicate that higher P. palmata inclusion improved hepatic function. Seaweed inclusion at 5 % also had positive effects on body lipid content when compared to the control diets. In conclusion, the findings demonstrated that P. palmata can be a suitable feed supplement in Atlantic salmon (S. salar) diets.