WHY CONDUCT SURVEILLANCE FOR PNEUMOCOCCAL DISEASE? Worldwide, infections with Streptococcus pneumoniae are among the leading causes of illness and death among infants and young children, persons with chronic medical conditions, and the elderly. In the United States, pneumococcal infections cause an estimated 3000 episodes of meningitis , 50,000 episodes of sepsis, 120,000 episodes of pneumonia, and as many as seven million cases of otitis media each year (1). The mortality rate for invasive pneumococcal infections (infections of blood or other sterile sites) is high ( 15% to 20%) among adults ; among the elderly, mortality can reach 40%. Despite its public health importance, until recently few public health agencies have included pneumococcal disease as a part of routine disease surveillance. However, with the emergence of drug-resistant Streptococcus pneumoniae (DRSP), the need for information about disease trends has increased. In some settings, local surveillance data, which include reporting of antimicrobial susceptibility results, can help cl inicians with treatment decisions; at a higher level, regional or national trend information can guide those drafting treatment guidelines . As treatment of pneumococcal infections becomes more difficult, renewed efforts should focus on preventing disease with pneumococcal vaccines; public health practitioners can use surveillance data to target vaccination programs and to measure program impact. This article examines the issues surrou nding survei llance for pneumococcal disease and describes surveillance systems in use in the United States. In add ition, the article reviews the epidemiology of pneumococcal disease and the emergence of drug-resistant infections, emphasizing surveillance findings.