Familial Hemophagocytic lymphohistiocytosis (FHL) is a rare autosomal recessive disease. It generally appears in childhood but atypical forms are also seen in adults. FHL is characterized by an excessive inflammatory response due to defects in NK and T-lymphocyte cytotoxicity. Clinical and biological diagnostic criteria are defined by the Histiocyte Society. Treatment includes the suppression of the excessive immune response followed by a hematopoietic stem cell transplant (HSCT). Diagnosis of FHL should include a genetic study in the proband and siblings to allow for preemptive measures.