We studied clinical characteristics and prognosis in acute stoke patients with diabetes mellitus registered on the Japanese Standard Stroke Registry database. A total of 16,630 acute stroke patients admitted to 56 hospitals in Japan. They were examined as to their stroke types, risk factors, their severity of stroke according to the NIH Stroke Scale (NIHSS) and Japan Stroke Scale (JSS), and outcomes by the modified Rankin Scale (m-RS). The incidence of subarachnoid hemorrhage was relatively high in the group of patients who had neither hypertension nor diabetes, and the incidence of brain hemorrhage was higher in the group of patients who had hypertension without diabetes. The frequencies of lacunar infarct and atherothrombotic infarct were also higher in the group of patients who had both hypertension and diabetes. In the diabetic group without hypertension, there were less numbers of hemorrhagic stroke. The ratio of good prognosis (m-RS 0-1) was significantly smaller in the diabetic patients with lacunar infarction, cardioembolic infarction, and subarachnoid hemorrhage. Additionally, there was significantly more stroke recurrence in the diabetic patients (33.0% vs. 26.9%, p<0.0001). The diabetic patients who received insulin therapy (-0.8 +/- 7.4), diet therapy (-0.4 +/- 9.4), or oral medicine (-0.9 +/- 7.2), showed significantly less improvements in the NIHSS compared to the non-diabetic patients (-1.6 +/- 8.2), respectively. Moreover, the poor-management diabetic patients showed significantly less improvements in the JSS compared to non diabetic patients (3.8 +/- 7.7 vs. 4.8 +/- 8.6, p<0.005). In conclusions, stroke patients with diabetes mellitus showed more stroke recurrence and resulted in poorer functional recovery compared to patients without diabetes.