A retrospective study was undertaken on onset of symptoms in 667 cases of stroke. All strokes occurred out of hospital. There were 382 males and 285 females, observed from 1971-1988. The 667 cases of stroke consisted of 508 cases of cerebral infarction and 159 cases of cerebral hemorrhage. The data, analyzed by the single cosinor method, demonstrate a significant circadian, circaseptan, and circannual rhythmicity in the occurrence of stroke. The peaks occur in the morning hours, in the weekend, and in winter. Cerebral hemorrhages do not have a circadian rhythmicity in their occurrence, while they do present circaseptan and circannual rhythmicity. Cerebral infarctions present circadian, circaseptan, and circannual rhythms. No difference was found between males and females. The possible factors involved in temporal distribution of stroke are discussed. These observations could be useful for a better understanding of the pathogenesis and treatment of stroke.