Systemic lupus erythematosus (SLE) patients are at increased risk of thrombosis and cardiovascular diseases. Aspirin is an effective treatment option for these patients. The aim of this study was to investigate the presence of aspirin resistance in SLE patients. We studied aspirin resistance in 33 SLE patients and nine healthy controls by using a Multiplate (R) impedance aggregometer (Dynabyte GmbH, Munich, Germany). Twenty-six SLE patients were on regular aspirin treatment. Aspirin resistance was found in five (19.2%) out of 26 patients who were on aspirin treatment. When the tests were repeated by adding acetylsalicylic acid in the medium, all of these patients became responsive to the aspirin. SLE disease activity, body mass index, smoking status, and the presence of anticardiolipin antibodies or positive lupus anticoagulant test results were no different in patients with or without aspirin resistance. (p>0.05 for all). Our results suggest that there may be a considerable number of SLE patients with aspirin resistance.