The tonsillitis has long been one of the most common disease in the otolaryngologic field. 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 tonsillitis who have been inadequately treated. We studied retrospectively 71 patients who had been diagnosed as acute tonsillitis and 82 patients who had been diagnosed as peritonsillar abscess and had admitted in our department of the Ulsan Dong Kang Hospital from January, 1995 to September, 1997. Especially in the bacteriologic studies, we compared acute tonsillitis and peritonsillar abscess with chronic tonsillitis. The following results were obtained： 1) The sex distributions of acute tonsillitis were 47 males(66%) and 24 females(34%) cases, but 57 males(70%) and 25 females(30%) in cases of peritonsillar abscess. There were predominant in male and frequently affected in second and third decades in 53 cases(76%) of acute tonsillitis and 56 cases(68%) of peritonsillar abscess. 2) It was same found in each season. 3) The duration from onset of symptom to visit in our department was 3.92 days in cases of acute tonsillitis and 5.95 days in cases of peritonsillar abscess in average 4) The major symptoms were sore throat, swallowing difficult. And others were fever, fatigability, dysarthria, trismus, headache, otalgia. 5) Among the 71 cases of acute tonsillitis and 82 cases of peritonsillar abscess, most temperature of patients at visit were 36.6-37.5 $^{circ}C$ in each 36 cases(51%), 57 cases(70%). 6) In each disease, 35 cases(47%), 45 cases(75%) consisted of single infection and 39 cases(53%), 15 cases(25%) consisted of mixed infection. In acute tonsillitis, 111 strains were isolated from 74 cases, the most common strain was 69 strains(62.2%) of $alpha$-hemolytic streptococci. In the peritonsillar abscess, 77 strains were isolated from 60 cases, the most common strain was 49 strains(63.6%) of $alpha$-hemolytic streptococci. In chronic tonsillitis, 563 strains were isolated from 382 cases, the most common strain was 334 strains(50.3%) of $alpha$-hemolytic streptococci. 7) In acute tonsillitis and peritonsillar abscess, the most common leukocyte levels were reported with 10, 000-15, 000/$mu$L in 23 cases(32%). The CRP levels were reported with abnormal findings in 61 cases(97%), 63 cases(95%) above 0.3 in each cases.