In systemic lupus erythematosus (SLE), the most commonly encountered finding related to platelets is thrombocytopenia whereas thrombocytosis is rarely reported. Our aim here was to reveal the type and the frequency of thrombocytosis in SLE patients along with its causes. Data of patients were evaluated retrospectively. Patients who had a platelet count of > 450,000/mm(3) (> 450 x 10(9)/L) in at least two subsequent counts and lasting more than 6 months during the follow-up were considered to have "persistent thrombocytosis". Peripheral smear results of patients with thrombocytosis were analyzed, and spleen imaging was performed for autosplenectomy/hyposplenism to patients with persistent thrombocytosis. A total of 205 patients with SLE were included in the study [196 (95.6%) female, mean age 41.5 years]. Out of 12 patients (5.9%) with thrombocytosis, 9 (4.3%) had transient thrombocytosis and 3 patients (1.4%) had persistent thrombocytosis. Of those with transient thrombocytosis, 5 were associated with iron deficiency anemia (IDA), 2 to polyarthritis, and the remaining 2 to digital ischemia and/or cutaneous vasculitis. Of three patients with persistent thrombocytosis, one was identified to have had splenectomy due to resistant immune thrombocytopenic purpura, and the other two (0.9%) patients had autosplenectomy. The only independent risk factor for the development of thrombocytosis was the presence of cutaneous vasculitis (OR 10.79 (95% CI 2.14-54.47), p = 0.0004). During the course of SLE, frequency of thrombocytosis is similar to that of the general population and the most common cause is reactive thrombocytosis. If the thrombocytosis was persistent, rheumatologist must consider that the patient may have autosplenectomy/asplenia/hyposplenism.