To investigate 35-year epidemiological trends in tonsillectomy and adenotonsillectomy. STUDY DESIGN/SUBJECTS: Cross-sectional survey. Subjects included all patients from birth to age 29 years who had tonsillectomy or adenotonsillectomy from 1970 to 2005. Study included 8106 patients (median age 8.0 years; range, 6 months to 29 years; male 3646 patients [45%]). Overall tonsillectomy incidence increased from 126 (95% confidence interval [CI], 111-140) per 100,000 person-years in 1970 through 1974 to 153 (95% CI, 139-166) in 2000 through 2005. A dominant factor, adenotonsillectomy incidence rose sharply from 243 (95% CI, 223-261) per 100,000 person-years in 1970 through 1974 to 485 (95% CI, 462-509) in 2000 through 2005. The indication of upper airway obstruction increased from 12 percent of patients in 1970 to 77 percent in 2005. Epidemiological trends in tonsillectomy and adenotonsillectomy have shifted substantially. Overall numbers have increased, and surgical indications have shifted from infection to upper airway obstruction.