The occurrence and significance of haematological abnormalities were analysed in 126 prospectively studied patients with systemic lupus erythematosus. Haemolytic anaemia occurred in 13 per cent, neutropenia in 47 per cent, lymphocytopenia in 20 per cent and thrombocytopenia in 27 per cent of all patients. Patients with haemolytic anaemia were less likely to have serositis, but no differences in the incidence of renal or cerebral manifestations were found between the various groups. Infections were mainly associated with the use of corticosteroid therapy. Life-table analysis showed no adverse influence on survival of haemolytic anaemia, neutropenia or lymphocytopenia, but late onset thrombocytopenia was associated with a decreased survival. No relationship was found between thrombocytopenia and the presence of antiphospholipid antibodies or the occurrence of thromboembolic events. We conclude that late onset thrombocytopenia in patients with systemic lupus erythematosus is associated with a decreased probability of survival but this could not be attributed to thromboembolic events.