Confusion surrounds the entity known as "lethal midline granuloma". Partly responsible is the lack of specificity in this term. "Polymorphic reticulosis" has been used as a term to describe the morphology of the disease. Thirty-two cases illustrate the protean features of this disease. Although it commonly presents in the head and neck, other sites such as the lungs, kidneys, skin, and gastrointestinal tract may be involved, either alone or in conjunction with lesions of the head and neck. Clinically, it is easily confused with Wegener's granulomatosis. Histopathologic differentiation, however, is both feasible and important. Wegener's granulomatosis is treatable with steroids with or without cyclophosphamide; polymorphic reticulosis confined to one site responds to irradiation. In polymorphic reticulosis, thhe best results of treatment are obtained in localized lesions of the upper airway treated early with irradiation; a poorer outcome is associated with multifocal involvement, which necessitates systemic therapy.