Crohn's disease (CD) is an idiopathic chronic inflammatory gut disease with frequent extragut inflammatory manifestations in the eyes, orbit, lungs, joints, and skin. A bacterial cause of CD is suspected, but cultivation of a specific pathogen has not been forthcoming. Mollicute-like organisms (MLOs) were recently reported to cause human chronic ocular inflammatory disease. Inoculation of this MLO into mouse eyelids produced chronic progressive granulomatous ocular and orbital inflammatory disease. In addition, MLOs disseminated to produce similar disease in the gut, heart, and lungs. MLOs are noncultivable cell wall-deficient bacterial pathogens. Because they also pass bacteria-retaining 0.450-micron filters, they can be overlooked or confused with viruses. Because MLOs have a characteristic ultrastructural appearance, they can be identified in diseased cells with the use of a transmission electron microscope. MLOs parasitize and destroy leukocytes. They alter the nucleus, replace the cytoplasm, and destroy organelles. MLO-caused disease is treatable by certain antibiotics. This report describes MLO-parasitized vitreous lymphocytes, monocytes, and polymorphonuclear leukocytes from three patients with CD who had chronic uveitis. The results indicate that MLOs probably caused the uveitis of these patients with CD. The gut as the possible source of the MLO is suggested. Rifampin therapy of Crohn's and MLO-caused disease is discussed.