The paper presents two cases of familial hemophagocytic lymphohistiocytosis in one family. The first case is the first-born female child with symptoms of an abrupt onset of hepatic failure and encephalopathy at the age of 2.5 months, and the second case is the third-born male child from the fourth pregnancy who died in his first month with a similar clinical manifestation. By means of histological examination, a diffuse proliferation of histiocytes of benign appearance with numerous phagocytized erythrocytes in the cytoplasm was found in both patients. These infiltrates existed in numerous organs and tissues of the body, but they were mostly visible in the spleen, liver, lymph nodes and in the bone marrow. The course of the disease is rapidly progressive with an up to now insufficiently explained etiology of the disease, with the existence of an autosomal recessive type of inheritance and defects in cellular and humoral immunity.