OBJECTIVES:To investigate the prevalence, clinical characteristics, and prognosis of thrombocytopenia (TP) in Chinese patients with systemic lupus erythematosus (SLE). METHODS:The study was conducted based on the Chinese SLE Treatment and Research group (CSTAR) registry. Thrombocytopenia was defined as the platelet count<100,000/mm3 at enrollment. Severe thrombocytopenia was defined as the platelet count<50,000/mm3. The prevalence of SLE-related TP, the associations of thrombocytopenia with demographic data, organ involvements, laboratory findings, disease activity, damage, and mortality were investigated. RESULTS:Of 2104 patients with SLE, 342 patients (16.3%) were diagnosed with thrombocytopenia. The prevalence of neuropsychiatric SLE, vasculitis, myositis, nephritis, mucocutaneous lesions, pleuritis, fever, leukocytopenia and hypocomplementemia were significantly higher in patients with thrombocytopenia (p<0.05). SLE disease activity index (SLEDAI) was significantly higher in patients with thrombocytopenia (p<0.05). Multivariate analysis showed that leukocytopenia (OR = 2.644), lupus nephritis (OR = 1.539), hypocomplementemia (OR = 1.497) and elevated SLEDAI (OR = 1.318) were independently associated with thrombocytopenia (p<0.05). Long disease duration (OR = 1.006) was an independent risk factor of severe thrombocytopenia, while anti-rRNP (OR = 0.208) was an independent protective factor of severe thrombocytopenia (p<0.05). Long disease duration was an independent risk factor of mortality in patients with thrombocytopenia (RR = 1.006). The 6-year survival of patients with thrombocytopenia was significantly lower than patients without thrombocytopenia (88.2% vs. 95.5%). CONCLUSIONS:Thrombocytopenia was a common manifestation of SLE and was associated with leukocytopenia, nephritis and severe disease activity. Severe thrombocytopenia tended to occur in long-term and relatively inactive SLE. Patients with SLE-related thrombocytopenia has a decreased long-term survival rate. Long disease duration was an independent risk factor of mortality in patients with thrombocytopenia.