We developed and validated a patient-reported outcome measurement for measuring the severity of symptoms and efficacy of different treatment modalities in patients with peritonsillar abscess (PTA).A 19-item questionnaire was constructed using a five-point Likert scale. Fifteen to 40-year-old patients with PTA treated at two ear-nose-throat departments completed the survey. Healthy students served as controls.A total of 51 PTA patients and 76 controls were included. Twelve items had appropriate inter-item correlations (in the 0.25-0.75 range) and high mean scores (> 3.5) among patients and were therefore included in the final tool, coined the peritonsillar abscess assessment tool (PAAT)-12. The patients' mean PAAT-12 score was 49.0 (95% confidence interval (CI): 46.8-51.1) at the time of inclusion compared with 14.2 (95% CI: 13.7-14.7) for controls (p less-than 0.001). The Cronbach's alpha coefficient for the questionnaire was 0.86. The standard error of measurement was 4.98, the intraclass correlation 0.88 and the Spearman correlation test-retest reliability 0.79.The reliability and validity of the PAAT-12 were very high. The PAAT-12 is the first validated tool for measuring the severity and duration of symptoms from the perspective of PTA patients and for quantifying and comparing different treatment modalities in PTA patients.Overlærer Svend Hansens Fond.The study was approved by the Danish Data Protection Agency (#1-16-02-356-19).