Subacute necrotizing lymphadenitis (SNL) is a well documented and unique clinicopathologic entity, although its etiology and pathogenesis have not been clearly established. Microscopically, cortical and paracortical necrotizing lesions with karyorrhexis, abundant nuclear debris and infiltration of large mononuclear cells are characteristic. This study analyzed the common clinical and pathological features of 118 patients with SNL and the nature of the mononuclear cells. Patients were generally young women and revealed cervical lymphadenopathy with tenderness, fever, leukopenia and elevation of the erythrocyte sedimentation rate. Features of the adjacent uninvolved area in the lymph node included a starry sky pattern, follicle centers, sinus histiocytosis or aggregation of foamy histicoytes. There was an inverse relationship between the extent of necrosis and of histocytic infiltration but not between the extent of necrosis and the duration from the onset of symptoms to the diagnosis. Immunohistochemically the infiltrated mononuclear cells of the affected foci were T lymphocytes and histiocytes. The clinical, histological and immunohistochemical features suggest that SNL represents a hypersensitivity reaction to certain infectious agent without forming granuloma.