Edwardsiella tarda was isolated from the peritoneal exudate of a Steller's sea lion (Eumetopias jubata) with peritonitis resulting from a perforating colonic ulcer; from the liver of a harbor porpoise (Phocena phocena) with metritis and peritonitis sequela to dystocia; and from the liver of a California sea lion (Zolophus californianus) with peritonitis following fracture and necrosis of a lumbar vertebrae. These findings indicate E. tarda is a common opportunistic invader in sick or injured marine mammals.