Defective apoptosis caused by mutations of the Fas gene can lead to an autoimmune lymphoproliferative syndrome (ALPS). The main autoimmune manifestations are haematological: hemolytic anemia, thrombocytopenia and neutropenia. We described 3 patients with ALPS presenting as a lymphoproliferative syndrome associated with a Coomb's negative autoimmune hemolytic anemia and dyserythropoiesis predominating on the more mature erythroblasts. Fas apoptosis deficiency was evidenced in the 3 patients by the demonstration of an increased number of CD4(-)CD8(-)TCRalphabeta(+) T cells, a decreased apoptotic response of activated T lymphocytes to anti-Apo 1-3 monoclonal antibody and the presence of a heterozygous mutation of the Fas receptor gene.