We studied the relation between outdoor temperature and mortality rates from cardiovascular disease in Taiwan from 1981 to 1991. In 11 years, there were 30,085, 21,750, and 39,818 deaths from coronary artery disease, cerebral infarction, and cerebral haemorrhage, respectively, among 7.6 million residents aged 25 and over in selected areas where climate was recorded. A temperature-mortality relation was especially apparent in the elderly. A U-shaped relation was observed between temperature and mortality from coronary artery disease and cerebral infarction. The range corresponding to least deaths from coronary artery disease (26-29 degrees C) and cerebral infarction (27-29 degrees C) was higher than that in countries with colder climates. In the elderly, the risk of cerebral infarction at 32 degrees C was 66% higher than that at 27-29 degrees C; the risk increased by 3.0% per 1 degree C reduction from 27-29 degrees C. The risk of coronary artery disease at 32 degrees C was 22% higher than that at 26-29 degrees C; below 26-29 degrees C, the risk increased by 2.8% per 1 degree C reduction. Mortality from cerebral haemorrhage decreased with increasing temperature at a rate of 3.3% per 1 degree C. These results imply a pathophysiological difference between thromboembolic and haemorrhagic cardiovascular diseases. Poor thermoregulation in older people may precipitate cardiovascular disease events.