There is growing evidence that a variety of corneal disorders may be expressions of altered immune mechanisms. Phlyctenular keratoconjunctivitis is probably such a condition. Typically described as arising from hypersensitivity to tuberculin protein, other antigens clearly may participate, particularly staphylococcus products. When corneal involvement occurs, it need not be confined to the peripheral cornea. The symptoms of the process may be disproportionate to obvious findings and so exaggerated as to suggest a psychiatric disorder. Resultant visual deficits, if the disease is corneal, progressive, unrecognized, and untreated may be profound. Representative examples of this disease are cited. Immune mechanisms are reviewed. The importance of recognizing the characteristic sign and symptom complex is stressed. Appropriate diagnostic studies and treatment regimens are presented.