This book summarizes findings from the National Health and Nutrition Survey Epidemiologic Follow-up Study (NHEFS) for persons 55 years of age and older at initial examination. This is the first prospective study of health and health-related behaviour in a representative sample of the US population. Included in the follow-up study approximately 10 years later were all 14,407 participants who were examined at baseline in 1971-1974 (National Health and Nutrition Survey I-NHANES I). This book reports on the 5,215 individuals who were 55-74 years of age at baseline and who could be traced for further examination. The prospective nature of this research permits the authors to estimate the incidence of new disease, to examine changes in health related behaviour over time, and to access the probability of subsequent disease, given the presence of risk factors at baseline. Their analyses provide new insights into disease causation and outcome in an aging population in the US.