- Objectives To describe the epidemiologic, microbiologic, clinical and therapeutic aspects of acute mastoiditis (AM) in children <15 years of age during the 4-year period (2009–2012) following the introduction of pneumococcal conjugate vaccines in Israel. Patients and methods The medical records of all children with a discharge diagnosis of AM were reviewed. Results A total of 66 AM episodes occurred in 61 patients. Forty-four (66.6%) cases occurred among patients <4 years, recent acute otitis media (AOM) history was reported in 27.1% and 28.8% patients received previous antibiotics for AOM. Postauricular swelling, postauricular sensitivity, protrusion of auricle and postauricular edema (93.8%, 90.6%, 85.9% and 95.7%, respectively) were the most common signs of AM. Leukocytosis >15 000 WBC/mm3 was found in 39 (59.1%) cases. Cultures were performed in 52/66 episodes (positive in 27, 51.92% episodes), with recovery of 32 pathogens. The most frequently isolated pathogens were Streptococcus pneumoniae (15/52, 28.85%), Streptococcus pyogenes (9, 17.3%) and nontypeable Haemophilus influenzae (5, 9.62%). Eight (53.3%) S. pneumoniae isolates were susceptible to penicillin. Mean incidence of overall and pneumococcal AM were 11.1 and 2.58 cases/100 000, with no significant changes during the study years. Surgical intervention was required in 19 (28.8%) patients. Conclusions (1) AM occurs frequently in patients without previous AOM history and with no previous antibiotic treatment; (2) S. pneumoniae and S. pyogenes continued to be the main etiologic agents of AM during the postvaccination period; (3) No changes were recorded in overall AM incidence and in pneumococcal AM incidence during the postvaccination period.