A nonsmoking woman, aged 44 years, presented with transient right-sided hemiparesis. CT showed leukoen- cephalopathy without infarction (figure). Blood pres- sure was normal. Blood count, plasma glucose levels, C-reactive protein, renal/liver function tests, cardiac enzymes, atrial natriuretic factor, HIV/syphilis/hepatitis B and C serology, and lactic acid levels were normal. Low-density lipoprotein (LDL) cholesterol levels were slightly elevated (1.25 g/L). Screening tests for pro- thrombotic disorders (serum fibrinogen, D-dimer, fibrin degradation products, antithrombin III level, protein C and S level, factor V Leiden, prothrombin gene mutation, antiphospholipid antibodies) were normal. Carotid duplex scanning, transthoracic echocardiography, and 24-hour Holter ECG were normal. Acetylsalicylic acid 160 mg once daily was started.