A substantial proportion of vaccine-preventable diseases occur among adults. Each year, there are more than 20,000 influenza-associated deaths during epidemics, approximately 40,000 deaths related to pneumococcal disease, and one to five cases of diphtheria. More than 300,000 hepatitis B infections occur annually, mostly in patients 15 to 29 years old. From 1982 to 1986, 96% of patients with tetanus were age 20 and older. Among young adults, 5% to 20% are susceptible to rubella and measles, and outbreaks occur where these persons congregate. Most adults are not immunized, despite recommendations for vaccines against these diseases. Vigorous efforts are needed to implement strategies to reduce disease incidence, morbidity, and death among adults.