Importance: Treatment of low-stage tonsil cancer with radiotherapy is common, but the type of diagnostic procedure prior to radiotherapy varies. This study uses the Surveillance Epidemiology and End Results (SEER) registry to determine whether tonsillectomy or other surgical procedures prior to radiotherapy have an impact on outcome. Objective: To demonstrate whether tonsillectomy adds oncologic advantage over biopsy alone in stage I or II tonsil cancers prior to definitive radiotherapy. Design: Retrospective study of the SEER program. Participants: A total of 524 patients with stage I and II primary tonsil carcinoma diagnosed during the period 1988 through 2006 who received definitive radiation treatment. Main Outcomes and Measures: Hazard ratios, 5-year disease-specific survival (DSS), 5-year overall survival (OS), and Kaplan-Meier survival curves. Subgroup univariate and multivariate analysis of survival compared the following variables: sex, T category (T1 vs T2), year of diagnosis (1988-2003 vs 2004-2006), and surgical status (preradiation tonsillectomy vs biopsy only). A log-rank test compared Kaplan-Meier survival analysis for the surgical status subgroups. Results: Statistically significant contributors to survival (DSS and OS) included age (P < .001, DSS), surgical status (P =.001, DSS), and year of diagnosis (P =.02, DSS). Treatment with radiation after tonsillectomy yielded a 5-year OS of 83% (95% CI, 77%-88%) and a 5-year DSS of 90% (95% CI, 84%-93%). This compares with an OS of 64% (95% CI, 54%-71%) and DSS of 76% (95% CI, 68%-82%) for radiation therapy after biopsy alone. Conclusions and Relevance: SEER data suggest that tonsil resection prior to radiation therapy is associated with improved survival in low-stage tonsil cancer. Although selection bias is a likely factor in this analysis, the effect remains after controlling for age and year of treatment.