To report the experience of a large tertiary care pediatric center during a period of increasing Streptococcus pneumoniae antimicrobial resistance before the introduction of pneumococcal vaccine in Israel. Retrospective chart review of children diagnosed acute mastoiditis (AM) between January 1997 and December 2007. The children were divided into 4 age groups (6-11, 12-23, 24-35, and 36-40 months), and each group was compared with the others. A total of 198 AM episodes were recorded during the 10-year study period. The most prevalent pathogen was S. pneumonia, with a very low (15%) penicillin resistance rate (minimal inhibitory concentration ≥ 2). Complications were more prevalent in the 12- to 23-month age group. The number of AM cases increased during the study period. Penicillin resistance did not play an important role in determining the morbidity before the introduction of pneumococcal conjugate vaccine.