The authors examined the patterns of mortality from ischemic heart disease and cerebrovascular disease in Australia for men and women aged 30-84 years during the period 1950-1986 to assess the relative contributions of period and cohort effects on changes in the mortality rates. Death rates for ischemic heart disease increased from 1950 to the late 1960s and then declined. Although the relative magnitude of the decline was greater among younger age groups, decreasing mortality rates were experienced in all age groups, including the oldest. The period effect was dominant so that each successive cohort experienced lower age-specific mortality rates after the late 1960s. Death rates for cerebrovascular disease for both sexes and all age groups have declined since the early 1950s, although the rate of change was less in 1961-1971 and greater before and after this period. No cohort effect was demonstrated for either disease. Changes in diet, decreasing prevalence of cigarette smoking, and increasing treatment of hypertension throughout the period and improved coronary care from the late 1960s onward are all consistent with the mortality trends.