Scleritis is not a single clinical or pathologic entity. It has several distinct forms. A clinico-pathologic study of 41 cases of necrotizing scleritis suggests that these different histopathologic forms of disease may reflect different mechanisms of immunopathogenesis. These cases were divided into three main groups: (1) scleral inflammations associated with various systemic autoimmune diseases, including 11 cases of rheumatoid arthritis, three cases of Wegener's granulomatosis, one case of polychondritis, and one case of Goodpasture's syndrome; (2) infectious scleritis, consisting of four cases of herpes zoster ophthalmicus and two cases of pseudomonas scleritis; and (3) idiopathic scleritis, without evidence of systematic disorder, consisting of 19 cases. The first group exhibited predominantly necrosis of the sclera surrounded by granulomatous inflammation and vasculitis. None of these cases showed lymphoid follicles, or healing attempts manifested by proliferation of fibroblasts and blood vessels at the site of inflammation. The idiopathic group revealed few small foci of scleral necrosis and mainly non-granulomatous inflammation. In addition, there was evidence of proliferation of granulation tissue and lymphoid follicles in this group of eyes.