The purpose of this study was to present projections of the future population of diabetes patients, to discuss policy implications of these projections, and to suggest ways that these projections might be made more useful to medical professionals. Under the assumption that the incidence of diabetes in four age-groups will remain constant in future years, previous estimates of the incidence of diabetes will be applied to Bureau of the Census population projections to project the number of new cases of diabetes that can be expected in future years in each of these age-groups. The prevalence of diabetes will remain relatively constant at approximately 1 million patients in younger populations (less than 45 yr old) through the middle of the next century. As the post-World War II baby boom ages, the number of older diabetes patients (45 and older) will almost double from 6.5 million in 1987 to an estimated 11.6 million in the year 2030. Although there is little doubt that the aging of the population will increase the number of diabetes patients, the assumption of constant incidence rates is a very limiting one. These projections would be more useful for the planning of research and training if the incidence of diabetes could be estimated for more refined categories of demographic and medical characteristics.