Revaccination with the 23-valent pneumococcal polysaccharide vaccine (PPV) has remained controversial due to lack of immunological data and fear of side effects. We re-vaccinated 61 elderly patients (median age 75 years), who had a history of hospital treatment for pneumonia, with PPV on average 5.3 years after their primary vaccination. Revaccination resulted in significant increases of the geometric mean antibody concentration (GMC) and the geometric mean antibody fold increase (GMFI), although to lower levels than after primary vaccination. 36/61 (59%) of the patients responded with a GMFI of > or =2 to > or =2 of six serotypes. Local reactions to revaccination were common (63%), but mild, and there were no serious adverse events. We conclude that revaccination of elderly with PPV after 5-10 years is safe and induce a significant immune response in a majority of persons.