Hemophagocytic lymphohistiocytosis occurring as a primary or acquired disorder is a condition of chaotic and uncontrolled immune system stimulation. Cytotoxic cells and macrophages cause multiorgan damage, hemophagocytosis, and severe systemic inflammation. Clinical manifestations include a fever, organ enlargement, and weight loss. Laboratory tests show bicytopenia or pancytopenia, cytolysis and cholestasis, serum ferritin elevation, and clotting disorders. The reference standard for the diagnosis remains the presence in histological specimens of hemophagocytic macrophages, which may be lacking early in the disease, leading to diagnostic challenges. Inherited forms produce symptoms in early childhood and are fatal in the absence of specific treatment. In adults, the clinical spectrum ranges from mild and self-limited hemophagocytic lymphohistiocytosis to rapidly fatal multiorgan failure. Many questions remain unresolved regarding the diagnosis and treatment in adults. This update is an attempt at providing answers.