Adult immunization is a neglected and underpublicised issue in Southeast Asia. Vaccine-preventable diseases cause unnecessary morbidity and mortality among adults in the region, while inadequate immunization results in unnecessary costs, including those associated with hospitalization, treatment, and loss of income. Childhood vaccination coverage is high for the EPI diseases of diphtheria, tetanus and pertussis; however, unvaccinated, undervaccinated, and aging adults with waning immunity remain at risk from infection and may benefit from vaccination. Catch-up immunization is advisable for adults seronegative for hepatitis B virus, while immunization against the hepatitis A and varicella viruses may benefit those who remain susceptible. Among older adults, immunization against influenza and pneumococcal infections is likely to be beneficial in reducing morbidity and mortality. Certain vaccinations are also recommended for specific groups, such as rubella for women of child-bearing age, typhoid for those travelling to high-endemicity areas, and several vaccines for high-risk occupational groups such as health care workers. This paper presents an overview of a number of vaccine-preventable diseases which occur in adults, and highlights the importance of immunization to protect those at risk of infection.