A 37-year-old male with a 20-year history of systemic lupus erythematosus (SLE) was referred to our hospital for an unruptured right middle cerebral artery (MCA) aneurysm. Right cerebral angiography detected a saccular aneurysm (9.6 × 7.1 mm) arising from the bifurcation of the right MCA, and a dilatation of the inferior trunk M₂ in which three small branches were involved. The MCA aneurysm was treated with neck clipping. The aneurysmal dilatation of the inferior trunk M₂ was treated with proximal clipping, followed by double superficial temporal artery-MCA anastomosis. The patient was discharged from our hospital without complications. This is an extremely unusual case of surgical flow reduction treatment using bypass surgery for a complicated cerebral aneurysm in a patient with SLE.