Autoimmune-thrombocytopenia was the striking feature in a patient with typical clinical symptoms of systemic lupus erythematosus (SLE), complement C4 deficiency, and positive lupus serology. However, myelodysplasia was found in the bone marrow and chromosome analysis revealed a deletion of the long arm of chromosome 5 (5q-anomaly), which was confirmed by a hemizygosity for the c-fms oncogene (CSF-1-receptor) on Southern blot. Autoimmune phenomena reported in conjunction with myelodysplastic syndromes (MDS), e.g., an elevation of antinuclear antibodies, are usually regarded as nonspecific. This case report suggests that SLE can occur in patients with MDS and that a concomitant autoimmune-thrombocytopenia may mask the typical signs of the 5q- syndrome.