The identification of Listeria monocytogenes as a cause of bacterial meningitis often has been missed due to its morphologic similarity to nonpathogenic diphtheroids. This gram-positive-staining micro-organism was seen in the spinal fluid specimens from two of seven patients. Specific identification was made by colony study on cultures grown from spinal fluid samples of each of the seven patients. The leukocyte count in the spinal fluid was not of diagnostic value. The signs and symptoms of the three infants and four adults did not differ from those of meningitis due to other agents. This organism also causes granulomatosis of the fetus and newborn infant, conjunctivitis, urethritis, and a type of infectious mononucleosis.