Seventy-five cases of Kikuchi's lymphadenitis, a self-limiting pseudomalignant condition, were reviewed to determine the spectrum of histologic findings. There were 55 females and 20 males; ages ranged from 9 to 57 years (mean, 25.5). Most patients presented with cervical lymphadenopathy (68 cases). Associated clinical findings were fever (20/52) and leukopenia (15/33). Serum antinuclear antibodies were negative in 15 patients among 16 tested. Among 32 patients with follow-up information, 31 remained well, including one who developed recurrence after 2 years. One patient died of fatal myocardial disease during the active disease. Histologically, the lymph nodes showed paracortical hyperplasia, often associated with a starry-sky appearance resulting from interspersed histiocytes and immunoblasts. The consistent finding was the presence of variable-sized discrete or confluent nodules in the paracortex composed of the following: (a) karyorrhectic and eosinophilic granular debris; (b) histiocytes, many of which were phagocytic and possessed distinctive peripherally placed crescentic nuclei and voluminous cytoplasm containing eosinophilic or karyorrhectic debris (for which we propose the designation crescentic histiocytes), mixed with nonphagocytic histiocytes having twisted or reniform nuclei which were often centrally placed; (c) plasmacytoid monocytes, which were medium-sized cells with eccentrically placed round nuclei and amphophilic cytoplasm; and (d) variable numbers of immunoblasts, which sometimes showed atypia such as irregular nuclear foldings and coarse chromatin. Neutrophils were absent or very sparse. In some nodules, coag-ulative necrosis was present in the center (45 cases). Foamy histiocytes were found in 23 cases, and they predominated in 11. Small clusters of plasmacytoid monocytes were noted in the paracortex in 40 cases. Perinodal inflammation was a common finding, and perinodal involvement by the karyorrhectic process occurred in 15 cases. In addition, we found a number of previously unreported features. Signet-ring histiocytes with clear or homogeneous lightly amphophilic cytoplasm and nuclei compressed into thin crescents, found in seven cases, could mimic signet-ring cell adenocarcinoma. In three cases, some germinal centers were involved by the karyorrhectic process. Foci of lymphocyte-depleted fibrovascular organization were present in eight cases, probably representing the resolving phase of the karyorrhectic process. Despite the broad morphologic spectrum, the intermingling of the distinctive crescentic histiocytes, karyorrhectic debris, and plasmacytoid monocytes in the form of nodules, together with the paucity of neutrophils, are the consistent findings that should permit a confident histologic diagnosis of Kikuchi's lymphadenitis.