The diurnal variation and activity during the onset of stroke were examined in more than 700 consecutive patients. 304 cases with hypertensive intracerebral hemorrhage (HIH), 214 cases with subarachnoid hemorrhage (SAH) and 201 cases with obstructive cerebrovascular disease (OCVD) were investigated about the time of onset. Concerning the activity during the onset, 296 cases with HIH, 215 cases with SAH and 198 cases with OCVD were examined. HIH occurred frequently between 1500-1800 hours, 0600-0900 hours and 1800-2100 hours. SAH occurred frequently between 0900-1200 hours, 1500-1800 hours and 1800-2100 hours. Both HIH and SAH were least likely to occur between 0000-0300 hours. OCVD exhibited a small peak incidence between 0900-1200 hours, but there were no differences between the groups for the other time periods. Both HIH and SAH were likely to occur frequently in the lavatory, while bathing and during meals. HIH also occurred frequently during physical work, while SAH occurred as frequently during mental work or housework as during hard physical labor. OCVD commonly occurred during sleep or relaxation. The relationship between diurnal variation in stroke and the circadian variation of blood pressure is discussed. The incidence of all three types of strokes during work was higher in the non-aged group (patients under 66 years) than in the aged group (patients over 66 years). HIH and SAH occurred associated with alcohol consumption more frequently in the non-aged group than in the aged group. It is likely that the difference of the time and of the activity during the onset between aged group and non-aged group reflects the difference of life-style between aged and non-aged people.