Langerhans cell histiocytosis (LCH) is a rare neoplastic disease of specific dendritic cells which belong to the monocyte-macrophage system. The association of LCH with autoimmune disease is extremely rare and to our knowledge its coexistence with systemic lupus erythematosus (SLE) has not been described so far. We report a case of LCH affecting liver, spleen and abdomen lymph nodes, which developed in an adult female six years after diagnosis of SLE treated for a long time with prednisone. Histology showed infiltration of characteristic Langerhans cells with folded, grooved or lobulated nuclei with fine chromatin. In the background there were eosinophils, lymphocytes and CD-68-positive histiocytes. The neoplastic cells were S100p-immunopositive, but stained negatively for CD1a--probably as the result of overfixation of consulted material. CD-68 was present mostly in macrophages. Ultrastructurally, the tumour cells presented structures consistent with Birbeck granules. Clonal origin of neoplastic cells was shown using the HUMARA-PCR assay. The disease was refractory to treatment with high doses of prednisone and vincristine but complete response was achieved after treatment with caldribine combined with cyclophosphamide.