Between 1945 to 1949 and 1975 to 1979, the average annual incidence of stroke declined by 45%, from 209 per 100,000 population to 115 per 100,000. For 1980 to 1984, the incidence rate of stroke was 17% higher than that for 1975 to 1979. This pattern--a decline followed by a recent increase--was also evident for cerebral infarction and intracerebral hemorrhage, but rates for subarachnoid hemorrhage remained stable throughout the period of study. The onset of the decline in incidence rates coincided with the introduction of effective antihypertensive therapy, but stabilized and increased rates were associated with continuing improvement in the control of hypertension. The stabilization and increase in the incidence rates of stroke coincided with the introduction of computed tomography (CT), which appeared to increase the detection of less severe strokes. The 30-day mortality for cerebral infarction decreased from 24% in 1945 to 1949 to 12% in 1980 to 1984, while that for intracerebral hemorrhage declined from 91% to 48% and that for subarachnoid hemorrhage from 64 to 42%. The dramatic decrease in mortality for intracerebral hemorrhage occurred during the 10 years when CT was first introduced and was due to the identification of small hemorrhages. These hemorrhages would have been classified as cerebral infarcts in the pre-CT era. Improved management of the secondary complications of cerebral infarction and subarachnoid hemorrhage may explain some of the improved survival for these two stroke subtypes.