Systemic lupus erythematosus (SLE) remains a disease of unknown origin, characterized by major alterations of both the cellular and the humoral arms of immunity. Hematological changes, including anaemia, leucopenia and thrombocytopenia, occur in more than one half of patients with this disease. Anaemia is the most common hematological abnormality seen in SLE. Its possible causes are anaemia of chronic disease (ACD), auto-immune haemolytic anaemia and hypoplastic anaemia. Leucopenia affects both granulocytic and lymphocytic lines and may be caused by autoantibodies. The influence of drugs, hypersplenism and marrow suppression are also possible. Thrombocytopenia occurs frequently and is almost invariably autoimmune. Patients with SLE are at increased risk of thrombosis. Haematological abnormalities in patients with this disease require careful long-term monitoring and prompt therapeutic intervention.