Several reports in the literature have documented an association of Langerhans' cell granulomatosis (LCG) with malignant lymphoma (ML). Seven additional patients are described, and different aspects of such an association are demonstrated. The diagnosis of LCG, made on the basis of routinely stained biopsy material, was supported by S-100 protein immunoperoxidase reactivity and/or the presence of Birbeck granules on electron microscopy. In six patients (cases 1 to 6) the LCG consisted of localized foci in nodes involved by ML. However, in one of these patients (case 1) focal LCG was again associated with ML in a later lymph node biopsy specimen from a different site, and in another patient (case 6) LCG subsequently developed in the skin and lungs. In the remaining case (case 7) pulmonary LCG developed one year after the diagnosis of Hodgkin's disease. Localized LCG in a lymph node involved by ML could represent an immune response to ML (cases 1 to 6 in the present study and 16 literature cases). The findings in case 6 indicate that such a response has the potential to become disseminated. Cases in which LCG and ML are found at different sites (case 7 in the present study and five literature cases) probably represent the coincidental association of two unrelated disorders. Finally, it has been postulated that, in rare instances, the development of Hodgkin's disease or malignant histiocytosis in a patient with LCG might represent malignant evolution of this hyperplastic process.