Changes in diet of cod (Gadus morhua) with increasing size were similar in the southern Gulf of St. Lawrence, Sydney Bight, Banquereau, and Western and Emerald banks. Small cod fed mainly on crustaceans and changed to a fish diet as they grew larger. Differences in species taken within the food groups seemed to depend on relative availability of the prey species. When cod reached sizes (ca. 50 cm) where they subsisted mainly on a fish diet, their main prey in the Gulf of St. Lawrence was herring (Clupea harengus) and on the Nova Scotia Banks it was sand launce (Ammodytes americanus). There were some seasonal differences in food eaten within areas and by depth.In the Western and Emerald bank areas, cod stomachs contained more food than haddock (Melanogrammus aeglefinus), up to two or three times as much for the large size-groups. Cod generally fed more heavily on pelagic crustaceans and fish whereas haddock took benthic animals, including annelid worms, molluscs, and echinoderms. When pelagic prey, particularly fish, were available to cod, there was the least overlap in food species taken by cod and haddock in the same area.