Peritonsillar abscess usually occurs in patients with recurrent tonsillitis or in those with chronic tonsillitis who have been inadequately treated. The abscess occurs when bacterial infection of the tonsil spreads to the potential peritonsillar space deep behind the tonsil and which is not rare and frequently encountered in clinical field in spite of decreasing incidence substantially since the advent of antibiotic therapy. A clinical observation was performed on 54 cases with peritonsillar abscess, who admitted to Department of Otolaryngology, College of medicine during past 6 years from 1982 to 1988. The obtained results were as follows ; 1) Male to femal ratio was 1.25 to 1. 2) Third decade(31.5%) were most frequently affected. 3) It was most prevalent in autumn(35.2%), summer, winter and spring are next in order. 4) The duration from onset to visit was 6.2 day in average. 5) Site of the abscess was right(44.4%), left(55.6%). 6) The major symptoms were sore throat in 54 cases(100%), swallowing difficulty in 46 cases(85.2%), trismus in 27 cases(50%), fever in 34 cases(63.%), headache in 26 cases(48.1%), and toothache in 38 cases(51.9%). And others were fatigability and phonation difficulty etc. 7) Among the 54 cases of peritonsillar abscess, bacteriological analysis was done in 40 cases and pathogenic organisma were isolated 35 case(87.5%), consisting of 26 cases of single infection and 9 cases of mixed infection and not isolated in 5 cases(12.5%). 8) Among the isolated 46 strains, α-hemolytic Streptococcus were 22 strains(55%), β-hemolytic Streptococcus were 4 strains(10%), γ-hemolytic Streptococcus were 2 strains(5.0%), Staphylococcus aureus were 3 strains(7.5%), nonpathogenic Neisseria were 8 strains(20%), Diphtheroid bacilli were 3 strains(7.5%), Klebsiella were 2 strains(5%), Enterococcus were 2 strains(5%). 9) All patients were treated with parenteral and oral antibiotics. Incision and drainage were performed in 41 patients(75.9%), 4 elective tonsillectomies and 2 immediate tonsillectomies were performed in recurrent peritonsillar abscess without complication. 10) Among the 54 cases of peritonsillar abscess, 5 cases(9.3%) have prior tonsillitis history, 5 cases(9.3%) have prior abscess history, 10 cases(18%) have frequent sore throat history, 4 cases(7.4%) have prior tonsillectomy history.