Seventeen cases of histiocytosis X presenting as lymphadenopathy, in which the initial diagnosis was based on lymph node biopsy, are reviewed, the characteristic histopathologic findings described, and the differential diagnosis discussed. Clinical evaluation reveals a broad spectrum of associated manifestations varying from solitary eosinophilic granuloma of lymph node to a disseminated Letterer-Siwe-like syndrome. Follow-up confirms the essentially benign nature of this disorder when defined by strict histologic criteria. The implications of these findings on the continuing controversy surrounding histiocytosis X are discussed.