We aimed to investigate the oral health of children in terms of the presence of dental caries, periodontal health, halitosis, and dentofacial changes in patients who had adenotonsillar hypertrophy related to mouth breathing and compared these findings with nasal breathing healthy and adenotonsillectomy-operated children. The patient group comprised 40 mouth-breathing children who were diagnosed with adenotonsillar hypertrophy, while the control group consisted of 40 nasal breathing children who had no adenotonsillar hypertrophy. Forty children who had undergone an adenotonsillectomy operation at least 1 year prior to the study were included in the treatment group. Oral examinations of all children were conducted, and the parents were asked about medical and dental anamnesis, demographic parameters, toothbrushing and nutrition habits, oral health-related quality of life (OHRQoL), and symptoms of their children. Demographic parameters, toothbrushing and nutrition habits, and the presence of bad oral habits did not differ between groups (
p
>
0.05
). Adenotonsillectomy is associated with a remarkable improvement in symptoms; however, some symptoms persist in a small number of children. The salivary flow rate, dmft/s, DMFT/S index, plaque, and gingival index scores did not differ between groups (
p
>
0.05
). The patient group showed higher rates of halitosis when compared with the treatment and control groups (
p
<
0.001
). Mouth breathing due to adenotonsillar hypertrophy caused various dentofacial changes and an increase in Class II division 1 malocclusion (
p
<
0.001
). It was shown that adenotonsillar hypertrophy does not negatively affect OHRQoL, it could be a risk factor for dental caries, periodontal diseases, and halitosis, but by ensuring adequate oral health care, it is possible to maintain oral health in children with adenotonsillar hypertrophy. Also, it is recommended that orthodontic treatment should start as soon as possible if it is required. In this context, otorhinolaryngologists, pedodontists, and orthodontists should work as a team in the treatment of children with adenotonsillar hypertrophy.