Several conditions have clinical and laboratory features that can mimic those present in Systemic Lupus Erythematosus (SLE). Some of these “SLE mimickers” are very common, such as rosacea which can be mistaken for the butterfly rash, while others such as Kikuchi disease, type-1 interferonopathies, Castleman's disease, prolidase deficiency, angioimmunoblastic T-cell lymphoma, Evans' syndrome in the context of primary immune deficiencies and the autoimmune lymphoproliferative syndrome are exceptionally uncommon. A proper diagnosis of SLE must therefore be based upon a complete medical history as well as on the adequate constellation of clinical or laboratory findings. While there is no single test that determines whether a patient has lupus or not, the search for auto-antibodies towards nuclear antigens is a key step in the diagnosis strategy, keeping in mind that ANAs are not specific for SLE. In case of persistent doubt, patients should be referred to reference centers with experience in the management of the disease.