Treatment algorithm for adult patients with HLH, including MAS-HLH. The HLH-94 pediatric treatment protocol is the consensus mainstay treatment of newborns, toddlers, and children up to 18 years of age, where genetic causes of HLH are enriched. Individual adaptation regarding the length and dosing of the HLH-94 treatment plan in adults is warranted. Allogeneic hematopoietic stem cell transplant (alloSCT) can cure primary HLH and may be applied in patients with high-risk hematologic malignancy as consolidation treatment or in relapsed HLH after successful salvage treatment. Treatment in adults cannot be standardized and needs tailoring according to the underlying condition and HLH-initiating trigger (infection, malignancy, autoimmune/autoinflammatory, drug induced, other causes). In relapsed/refractory (r/r) HLH, treatment intensification with chemotherapy, use of the anti-CD52 antibody alemtuzumab, cytokine adsorption using filter columns or plasma exchange, off-label treatment with the JAK2 inhibitor ruxolitinib, or the anti–IFN-γ antibody emapalumab have shown reasonable efficacy. BiTE, bispecific T-cell engager; CART, chimeric antigen receptor T cells; CHOP, cyclophosphamide, doxorubicin, vincristine, prednisone; CS, corticosteroids; DEP, doxorubicin, etoposide, methylprednisolone; IVIG, polyvalent immunoglobulins; Pat, patient. *Off-label in EBV-HLH.