Morganella morganii was isolated from the lung of a guinea pig. Necropsy revealed hemorrhagic consolidation of the lungs, and histological examination revealed bronchointerstitial pneumonia. M. morganii is a commensal gram-negative bacillus of the intestinal tract of humans, mammals and reptiles. Only few reports of M. morganii associated disease in animals are available in the literature. To the authors’ knowledge, this is the fi rst report of M. morganii associated disease in a guinea pig.