Acute otitis media (AOM) is a leading cause of visits to physicians and of antibiotic prescriptions for young children. We systematically reviewed studies on all-cause AOM episodes and physician visits in which impact was attributed to pneumococcal conjugate vaccines, either as efficacy or effectiveness. Of 18 relevant publications found, most used the 7-valent pneumococcal conjugate vaccine (7vCRM). The efficacy of 7vCRM against all-cause AOM episodes or visits was 0%-9% in randomized trials and 17%-23% in nonrandomized trials. In observational database studies, physician visits for AOM were already declining in the 3-5 years before 7vCRM introduction (mean change, -15%; range, +14% to -24%) and continued to decline afterward (mean, -19%; range, +7% to -48%). This vaccine provides some protection against OM, but other factors have also contributed to the recent decline in OM incidence. Future effectiveness studies should thus use better-controlled methods to estimate the true impact of vaccination on AOM.