Primary Epstein–Barr virus (EBV) infection causes infectious mononucleosis and hemophagocytic lymphohistiocytosis (HLH) in children, where EBV infects B and CD8+ T cells, respectively. We measured pro-inflammatory and anti-inflammatory cytokines in both diseases. Significantly higher concentrations of various mediators, including interferon-γ, neopterin, interleukin (IL)-6, IL-10, IL-18, and heme oxygenase-1, were observed in EBV-HLH. Because of their similarity to the profile of familial HLH, this profile was likely a consequence of HLH, but not ectopic infection. TNF-α levels were elevated in both diseases. Elevation of those mediators may contribute to the disease pathogenesis of EBV-HLH by activating and inhibiting host immune responses. Pediatr Blood Cancer 2013; 60: E46–E48. © 2013 Wiley Periodicals, Inc.