Causes of death of killer whales (Orcinus orca) in North America determined at necropsy included mediastinal abscesses, pyometra, pneumonia, influenza, salmonellosis, nephritis, Chediak-Higashi syndrome, fungus infection, ruptured aorta, cerebral hemorrhage and a perforated postpyloric ulcer. Captive females appear to have a higher rate of mortality than males. Growth rates for whales that died were greater than for those that survived.