The purpose of this study was to better understand the frequency and mechanisms of stroke recurrence after the stroke with no determined cause (NC). We prospectively studied consecutive patients with acute cerebral infarcts. We divided the patients into five groups (large artery disease [LAD], cardioembolism [CE], small artery disease [SAD], two or more causes [TMC], and NC) and registered recurrent strokes and prognosis for 1 year. Those in the NC group were compared with other subtypes. A total of 204 patients were included; 56 LAD, 22 CE, 62 SAD, 27 TMC, and 37 NC. During follow-up, there were 7 deaths and 31 first recurrent strokes. Patients of the NC group showed a significantly higher rate (30%) of recurrent stroke than those of other subtypes (LAD 16%; CE 14%; SAD 2%), and it was associated with the existence of mild stenosis (</=50%) on relevant artery or the stenosis of greater than 50% on nonrelevant artery. Occlusive lesions other than significant stenosis of relevant artery may play an important role in the development of stroke recurrence in patients of the NC group. Therefore, from the therapeutic and prognostic point of view, the detection of such occlusive lesions in patients with cryptogenic stroke may be needed.