Protein S deficiency is rare in systemic lupus erythematosus (SLE) and is generally associated with the presence of antiphospholipid (APL) antibodies. Lack of protein S can cause skin necrosis, but when it does it is generally in response to warfarin exposure. In this article, we describe the case of a patient who had not received warfarin and without APL antibodies who developed extensive skin necrosis due to protein S deficiency. It is important to investigate protein S deficiency in patients with lupus and extensive skin ulcers as it is a sign of arterial thrombosis and venous thromboembolism.