I research three topics in adult morbidity in the United States, focusing on two increasingly prevalent chronic diseases, diabetes and dementia. In the first essay, I investigate changes in age-specific diabetes prevalence across cohorts born in the 20th century and use the cross-cohort comparisons to generate model age patterns of diabetes prevalence and incidence. I show that most of the increase in diabetes prevalence over time is attributable to increases in age-specific prevalence from one cohort to the next. Because the risk of diabetes is embodied in cohorts, diabetes prevalence is likely to increase in the future even if the prevalence of risk factors such as obesity plateau. In the second essay, I use multiple-decrement life tables to estimate age-specific lifetime risks of dementia for a dementia-free person. I estimate that about a quarter of dementia-free 70-year-old males and a third of females will develop dementia in their lifetimes. Although interventions that delay dementia onset could substantially reduce dementia risk, the results indicate a widespread need to prepare for a life stage with dementia. In the third essay, I use recent advances in propensity-score matching techniques to estimate the association between incidence diabetes and subsequent accumulation of mobility limitations. Among observationally similar pairs of individuals, those who developed diabetes reported an average of 25% more mobility limitations at study exit than those who did not develop diabetes. My estimates of this association are smaller than those found in most of the existing literature, but they are likely less biased.