Abstract: In systemic lupus eryThematosus (SLE) various antibodies are produced against cells including platelets and result in thrombocytopenia. !n the literature, the incidence of thrombocytopenia varied from 7% to 52%, in seven series of SLE patients with a mean cumulative percentage of 14.5% (1-5 ). SLE patients referred to the Lupus Unit of the Rheumatology Research Center. Tehran University for Medical Sciences. (Shariati Hospital) during the period of 1975 to 1977 were included in this study. Thrombocytopenic patients were selected and 72 items were studied. The incidence of thrombocytopenia in Iranian SLE patients was 16.6%, which is similar to the mean cumulative percentage mentioned above. There was no difference in sex ratio between thrombocytopenic and nonthrombocytopenic patients. The same, was true for the mean age at the onset of the disease. !n 70% of patients there was mild to moderate thrombocytopenia (platelet from 50000 to 150000 mm3). The remaining (30%) had severe to very severe thrombocytopenia. !n 1.9% of patients had a previous diagnosis of idiopathic thrombocytopenic purpura (ITP). The following symptoms were seen more often in thrombocytopenic patients than in others: Hemolytic anemia (p<0.001), leukopenia (p<0.001), lymphopenia (p<0.001), splenomegaly (p<0.00007), and abortion (p<0.0006). For the followings the p value was less than 0.05: ESR > 100, positive FANA, positive Anti-dsDNA antibodies, positive VDRL, and positive anticardiolipin antibodies. All thrombocytopenic patients except one (previously splenectomized) were controlled by the medical treatment. Severe and very severe thrombocytopenia were controlled in 86% of cases by moderate to high dose steroids, with or without cytotoxic drugs. In 10% of cases, thrombocytopenia was controlled by a combination of chloroquine and low dose steroid (< 15 mg prednisolone daily). In 4%, other medical treatments (Danazol, etc.) were needed.