为了观察急性脑中风事件与昼夜节律的关系，我们分析4年来CT或MRI证实急性脑中风405例的发病时间。结果，172例（42．5％）发病集中分布于6时～12时，263例急性缺血性脑中风事件，122例（46．4％）亦发生于此期间，显著高于其它间期（P＜0．005），无论是出血性或缺血性脑中风（在24时～6时）发病显著低于其它间期（P＜0．005）。 In order to observe the relationship between acute stroke and circadian rhythm, we analyzed the onset time of 405 cases of acute cerebral apoplexy confirmed by CT or MRI in 4 years. Results: Of the 172 cases (42.5%), the incidence of acute cerebral apoplexy occurred from 6:00 to 12:00, and 122 cases (46.4%) also occurred during this period, which were significantly higher than those in other periods (P <0.005). The incidence of hemorrhagic or ischemic stroke (at 24 hours to 6 hours) was significantly lower than that of the other periods (P <0.005).