The incidence of peritonsillitis is not very well known. A retrospective study was performed at the Ear, Nose and Throat clinic (ENT) at the University Hospital of Orebro Sweden. We studied every case from 2002 to 2004 and related it to a well-defined catchment area of 179,200 inhabitants. We identified 283 events of peritonsillitis, of which 85 were defined as peritonsillar cellulitis (PTC). Peritonsillar abscess (PTA) was found in 198 events in patients between 7 and 82 y of age. 13 patients had 2 episodes of PTA during the study period. The overall incidence was 37/100,000/y. The highest incidence was found between 14 and 21 y of age, with 124/100,000/y. The male: female ratio was 1: 1. Affected females were younger than males (p=0.04), and the peak incidence was earlier for females. This may be due to differences in immunological response, owing to hormonal maturation. The annual incidence of PTA was higher in this study than found in previous studies, which is probably attributable to the fact that our study identified almost all cases in the population.