Background: Erdheim-Chester disease (ECD) is a rare non-Langerhans cells histiocytosis associated with intense immune activation. In our clinical center, an ECD patient was treated with anakinra, IL-1RA (interleukin-1 receptor antagonist), resulting in clinical improvement and major decrease of pathological fatigue. The aim of the study was to evaluate changes in cytokine profile and shift of immune cells estimated by fl ow cytometric analysis of ECD patient before, during initial stages of anakinra treatment as well as after treatment ceased in comparison to healthy donors. Methods: Singleplex reactions of 19 individual cytokines from serum of ECD patient were measured by FACS array. Flow cytometric analyses were performed on peripheral blood cells. Results: The most striking result is substantial decrease of IL-6 immediately after anakinra treatment started suggesting a major role of IL-1 pathway in ECD pathophysiology. As for fl ow cytometric analysis, increased number of CD16+ monocytes before treatment is a new finding. Conclusion: Our results suggest that IL-6 may be a marker of early treatment response of ECD patients treated with anakinra.