A new method of projecting increases in the number of dementia cases is described. This method is based on a statistical analysis of all published prevalence studies which shows that prevalence rate rises exponentially with age. The method can be easily applied to any age-specific population projections. When applied to Australia and New Zealand, the method shows that the increase in dementia will greatly exceed the total population growth rate, and even surpass the expected rise in the elderly group over the next third of a century. The method predicts that the Australian demented population will increase by 136-139% between 1984 and 2021, compared to a general population increase of only 42-54%. Over the period 1982 to 2016, the New Zealand demented population will grow by 96-100% against a rise of 18-26% in the general population. The validity of this method and its implication for future service demands are discussed.