Diabetes mellitus is the second major risk factor for ischemic stroke. Recent increase in atherothrombotic stroke appears to be related with recent increasing of diabetes. Diabetes is, however, a risk factor not only for atherothrombotic stroke but also for lacunar stroke because there is no difference in prevalence of diabetes between atherothrombotic and lacunar strokes. Diabetes can be a risk factor for cardioembolic stroke as well because the major cause of cardioembolic stroke is atrial fibrillation, and diabetes is a risk factor for stroke in patients with atrial fibrillation. Acute ischemic stroke should be classified into above three subtypes according to the brain and artery imaging as well as cardiac sources of embolism. In hyper-acute patients within 3 hours of onset and without early ischemic signs on CT or ischemic lesions less than one third of the hemisphere on magnetic resonance diffusion-weighted imaging, thrombolytic therapy with alteplase is indicated. In acute stroke patients later than 3 hours of onset, argatroban, heparin, and ozagrel are indicated for atherothrombotic, cardioembolic, and lacunar stroke, respectively. For stroke prevention, total management is required by simultaneous treatments for all risk factors existed. In secondary prevention for stroke, in addition to the more strict control of risk factors antithrombotic therapy is required, that is, antiplatelet therapy is indicated for non-cardioembolic stroke, and anticoagulant therapy is indicated for cardioembolic stroke.