Peritonsillar abscess occurs when bacterial infection of the tonsil spreads to the potential peritonsillar space deep behind the tonsil, and it usually occurs in patients with recurrent tonsillitis or in those with chronic tonsillitis who have been inadequately treated. Peritonsillar abscess, in spite of decreasing incidence substantially since the advent of antibiotic therapy, is not rarely experienced in the clinical field. A clinical observation was performed on 108 cases with peritonsillar abscess, who admitted to Department of Otolaryngology, SAH during past 10 years from 1980 to 1989. The obtained results were as follows ; 1) Male to female ratio was 2.4 to 1. 2) Third decade(33.3%) were most frequently affected. 3) It was most frequently found in summer(35.2%), spring, winter and autumn are next in order. 4) The duration from onset to visit was 5.8 days in average. 5) Left side was more frequently affected than right side(56 : 49). 6) The major symptoms were sore throat in 108 cases(100%), swallowing difficulty in 93 cases(86.1%), trismus in 93 cases (86.1%), fever in 80 cases(74.1%), fatigability 73 cases(67.6%), dysarthria 50 cases(46.3%). And others were headache and otalgia etc. 7) Among the 108 cases of peritonsillar abscess, bacteriological analysis was done in 87 cases and pathogenic organism were isolated 48 case(55.2%), consisting of 38 cases of single infection and 13 cases of mixed infection and not isolated in 39 cases(44.8%). 8) Among the isolated 60 strains, α-hemolytic Streptococcus were 36 strains(41.3%), β-hemolytic Streptococcus were 11 strains(12.6%), Staphylococcus aureus were 4 cases(4.5%), Staphylococcus epidermidis 3 cases (3.4%), H. influenza 3 cases(3.4%) Neisseria 2 cases(2.3%), Pseudomonas aeruginosa 1 case(1.1%). 9) All patients were treated with parenteral and oral antibiotics and incision and drainage were performed satisfactorily. 13 elective tonsillectomy and 2 immediate tonsillectomy were performed in recurrent peritonsillar abscess without complication. 10) Among the 108 cases of peritonsillar abscess, 6 cases(5.6%) have prior tonsillitis, 9 cases(8.3%) have prior abscess history, 28 cases(26.9%) have frequent sore throat history.