In this first study of adult Black Guillemot Cepphus grille diet in the Norwegian mainland, 62 of 63 birds caught incidentally in Lumpfish Cyclopterus lumpus gill nets in the north of the country in April-June 2012 and 2013 contained food remains in their stomachs. Fourteen prey taxa were identified and crustaceans were present in 90% of the stomachs containing food, with squat lobsters (sub-order Anamura) being most common (in 79%). Rock Gunnel Pholis gunnellus was present in 17 (27%) of the samples. The only other prey types to be found in more than 20% of the samples were sculpins (Cottoidei, probably Cottidae and Agonidae, in 13 samples = 21%) and remains of Caridean shrimps (also in 13 samples). There were no differences in the frequencies of taxa in the diets of immature and adult birds or of males and females.