The occurrence of disease in the remaining tonsil after unilateral tonsillectomy à chaudin the treatment of peritonsillar abscess, was studied in 536 patients. No patient had a history of previous severe tonsillitis at the time of the unilateral tonsillectomy, 6.1 per cent of the patients were readmitted for surgery of the remaining tonsil during the follow-up period. Ninety-seven per cent of these patients were younger than 30 years of age. Previous investigations have shown increasing frequency by age of pharyngitis after bilateral tonsillectomy. We suggest bilateral tonsillectomy in all cases of patients younger than 30 years old who suffer from peritonsillar abscess irrespective of previous tonsillar disease. Patients older than 30 should be treated with unilateral ablation, unless there is a clear indication for bilateral tonsillectomy.