Forteen cases of angioimmunoblastic lymphadenopathy were reviewed retrospectively, and histologic material was examined by various staining and histochemical techniques. The predominant morphologic features were effacement of nodal architecture, microvascular proliferation, and a polymorphous cellular infiltrate of immunoblasts, plasma cells, lymphocytes, and eosinophils. Immunofluorescence studies suggested the presence of cells elaborating a variety of immune globulins with an unpredictable pattern. The clinical course and treatment varied, perhaps partly reflecting the initial spectrum of diagnoses made in these cases before angioimmunoblastic lymphadenopathy was defined. Because systemic infection appears to be a major factor in the deaths of these patients whose immune competence is uncertain, the usual chemotherapy for malignant lymphomas may be too vigorous for this condition. At present, the cause of the condition is unknown.