The described clinical case presents 39-year-old patient with no clinically significant accompanying diseases. Since the beginning of October 2015, the patient has complained of fever, abdominal pain and generalized enlarged lymph nodes. Biopsy of axillary lymph node evidences Rosai-Dorfman-Destombes (RDD) disease. Treatment with corticosteroids has been started but with no clear influence on paraclinical activity and lymphadenomegaly. From the additionally made examinations, clinical laboratory data for malignant histiocytosis are found. According to literary data, in 27% of patients suffering from RDD, it transforms into malignant histiocytosis. The presented clinical case is interesting not only because of the registered clinical laboratory data of malignant histiocytosis but for the unclear diagnostic and prognostic importance of this phenomenon, as well