A method of treating active Systemic Lupus Erythematosus (SLE) in a patient by administering a clinically proven safe and clinically proven effective amount of an anti-IL-12/IL-23p40 antibody or an anti-IL-23 antibody, e.g., the anti-IL-12/IL-23p40 antibody ustekinumab, wherein the patient achieves a significant improvement in disease activity.