Background: Splenectomy has been performed to treat refractory autoimmune thrombocytopenia. However, some reports have suggested that an increased risk of thrombosis could be present in splenectomized patients. This study aims to evaluate the possibility of an increased risk of thrombosis after splenectomy in patients with systemic lupus and antiphospholipid syndrome. Methods: Thrombotic-related events in patients with systemic lupus erythematosus (SLE) and/or primary antiphospholipid syndrome (PAPS), before and after splenectomy for severe thrombocytopenia, were compared. Clinical data, laboratory investigations, and anticoagulation or antiaggregation treatment data were collected from the notes of outpatients attending three European centers. Results: Twenty patients who had had a splenectomy were identified: eight with SLE, five with PAPS, and seven with SLE and APS. The mean time between diagnosis and splenectomy was 3.1 years and mean follow-up was 6.5 years. There were no differences in anticardiolipin antibody titers, lupus anticoagulant, anti-DNA or anti-nuclear antibodies before and after surgery. The incidence of venous events before and after splenectomy was not significantly different. There was a trend towards an increase in the total number of arterial events post-splenectomy. In aCL-positive patients, and in the pre-splenectomy period, the total number of miscarriages was higher (p=0.017), as was the number of patients who had had a miscarriage (p=0.025). Conclusions: The total risk of thrombosis in patients with PAPS and SLE was not increased after splenectomy, but there was a trend towards an increase in the number of arterial events. Splenectomy induced long-term remission of thrombocytopenia (partial or complete) in all patients.