The occurrence of a secondary hemophagocytic lymphohistiocytosis/macrophage activation syndrome (HLH/MAS) after CAR T-cell infusion is very rare and mostly fatal. Treatment recommendations for such a complication are not yet established. Here, we report the dramatic recovery of HLH/MAS following tisagenlecleucel infusion in a young patient with relapsed acute lymphoblastic leukemia using etoposide phosphate (EP). We propose that monitoring for the occurrence of HLH/MAS should be part of surveillance after CAR T-cell infusion and that EP treatment appears to be useful to control this severe and rare complication.