Unsuspected tonsillar malignancy in routine tonsillectomy specimens is rare. A potentially increased risk of unsuspected tonsillar malignancy in adult patients presenting with peritonsillar abscess (PTA) was noted in a recent review. Furthermore, a literature search revealed several case reports concerning tonsillar malignancy presenting as PTA. Thus, the aim of the current study was to explore the prevalence of tonsillar malignancy in adult patients with PTA. A retrospective review of all adult patients undergoing tonsillectomy due to PTA from January 2001 to December 2012 at the Ear-Nose-Throat Department was performed. In 275 consecutive adult patients with PTA (median age 40 years, range 30-89 years), we identified one patient with unsuspected tonsillar malignancy (prevalence 0.3 %); a 40-year-old, previously healthy, male was diagnosed with acute myeloid leukaemia. Reviewing the literature, we identified 13 cases of tonsillar malignancy presenting as PTA (median age 49 years, range 2-66 years). Our data represents the only series of histological examined tonsillectomy specimens from PTA patients reported in the literature. We identified one case of unsuspected tonsillar malignancy in this relatively small series. We find it important to stress, that we had no knowledge of this patient before designing the study. Hence, the prevalence of 0.3 % is unbiased in this respect. More, and preferably, larger studies are needed to determine the prevalence with greater certainty. At present, no definitive conclusions can be made, but clinicians should be aware that PTA infrequently masquerade tonsillar malignancy.