Background/Aim. Antibiotics choice and the duration of their application in the therapy of acute odontogenic abscess is considered to be controversial. The aim of this study was to investigate the clinical efficacy of ampicillin in treatment of acute odontogenic abscess and to assess the antimicrobial susceptibility of the isolated bacteria in early phase of abscess development. Methods. This study included 60 patients with acute odontogenic abscess who were surgically treated (extraction of teeth and/or abscess incision) divided into two groups, ampicillin group and surgical group (without antibiotic treatment). Results. In the ampicillin group of patients treatment lasted on the average 4.67 days, while in the surgical group 6.17 days. A total of 78 bacterial strains were isolated from 60 patients. The most often bacteria were found to be Gram-positive facultative anaerobs (68/78). The most common bacteria isolated were Viridans streptococci (43/78). Susceptibility of isolated bacteria to ampicillin were 70.5%. Conclusion. Peroral use of ampicillin, after surgical treatment in an early phase of dentoalveolar abscess development, statistically significantly reduced the time of clinical symptoms of acute odontogenic abscess in comparison to surgical treatment only. The isolated bacterial strains in an early phase of dentoalveolar abscess development showed a high sensitivity to ampicillin.