We describe an outbreak of foodborne tonsillopharyngitis caused by group A streptococcus (GAS), a rarely reported event that occurred during a campus orientation meeting in Japan. Of 461 students and staff members who had eaten boxed lunches during a meeting at Kitasato University, 298 developed sore throat and/or fever, and 285 underwent medical examination. Amoxicillin was prescribed when throat culture specimens yielded GAS. The attack rate was 64.6%. T-25 GAS was isolated from 150 examined persons. Of 65 patients who received amoxicillin for 3 days, GAS was eradicated before the first follow-up throat culture in 46 (70.8%) cases. Susceptibility was demonstrated to penicillins, cephalosporins, and macrolides in 86 GAS isolates obtained more than once from a given patient. GAS strains isolated at various time points were indistinguishable by pulsed-field gel electrophoresis (PFGE), and prtF1 was present. GAS strains were often difficult to eradicate because of a short initial treatment period, patient compliance problems, and the presence of prtF1.