OBJECTIVE Recurrent acute tonsillitis in children under 4 years of age is usually viral, making antibiotic therapy inappropriate and the indication for tonsillectomy uncertain. Identifying those young children with bacterial infections is therefore important. The purpose of this study was to determine whether one-off streptococcal serologic testing is a useful tool in assessing recurrent acute tonsillitis in young children. METHODS We performed a retrospective study of 45 children (35 male and 10 female) under the age of 4 years who were found by a staff otolaryngologist to have recurrent acute tonsillitis over a 5-year period and had one-off serologic testing for anti-streptolysin O titers and anti-deoxyribonuclease B levels. Data were collected by chart review. RESULTS Three children (6.7%) had clearly positive titers for either one or both streptococcal antibodies. Children with negative serologic results were significantly less likely to have shown a significant response to antibiotic therapy for their acute episodes (26% versus 100%; p = .026). Nine children (20%) eventually underwent tonsillectomy, all of whom had negative serologic results. CONCLUSIONS Anti-streptolysin O and anti-deoxyribonuclease B levels may aid clinical evaluation of recurrent acute tonsillitis in young children in differentiating between those cases due to group A beta-hemolytic Streptococcus and those that are viral in origin.