An 85-year-old woman with the diagnosis of diabetic ketoacidosis developed septicemia during hospitalization. Cultures of the patient's blood revealed the presence of Gram-variable coccobacilli, later identified as Corynebacterium aquaticum. The microorganisms grew aerobically on blood agar plates after incubation overnight. The colonies were convex, non-hemolytic and slightly yellow-pigmented. No growth was observed on MacConkey and endo agar plates. The organisms were catalase-positive, oxidase-negative, motile, and oxidized glucose and mannitol. The morphologic and biochemical properties of Corynebacterium aquaticum should be considered for separation from related organisms such as Listeria monocytogenes, Corynebacterium species and oxidative Gram-negative rods that do not grow on MacConkey medium (Flavobacterium spp.).