In this paper we report findings on the diet of the harbour porpoise (Phocoena phocoena) in Danish, Swedish and Norwegian waters. The study is based on stomach contents from 247 porpoises bycaught or stranded between 1985 and 1990. Fish otoliths were identified and counted and other stomach contents recorded. A minimum of 30 species of fish were identified, representing 16 families. Off northern Norway, capelin (Mallotus villosus) was an important species (62% frequency of occurrence). In Scandinavian waters as a whole, herring (Clupea harengus) was the single most important species in the diet. Clupeidae and Gadidae were the most common prey families. Pelagic and mesopelagic fish were more important in the diet of the harbour porpoises in Norwegian waters, while benthic species were more important in Danish and Swedish waters. Cephalopods occurred in only seven (3.8%) of the stomachs and in low numbers per stomach. The smallest porpoise with food remains other than milk had a total body length of 100cm. The differences between the diet in the northern and southern part of the study area are related to the geographical distribution of some of the prey species, but can also be related to differences in bathymetry in the Norwegian area and the Danish and Swedish area.