<p>Obstructive sleep apnea due to tonsillar hypertrophy is accompanied by a higher prevalence of behavioral problems. This study compares the behavioral problems in children with adenotonsillar hypertrophy before and after adenotonsillectomy surgery. A descriptive-analytical cross-sectional study was conducted on 70 children aged 6 to 11, with grade 3 and 4 tonsillar hypertrophy. The Persian version of the Conners’ Parent Questionnaire was used to find the behavioral problems. Arterial blood oxygen saturation was evaluated and the questionnaire was completed before and six months after the surgery. Data were analyzed using paired *t*-tests in SPSS version 20. The McNemar test was used to compare the proportions of children with clinically significant symptoms before and after surgery. Normality was confirmed via Shapiro-Wilk test (<i>p</i> &gt; 0.05). The mean age of participants were 7.7 ± 1.6 years, 68.6% were male. Before the surgery, the arterial blood oxygen saturation was 97.3% and increased to 98.1% after the surgery (<i>P</i> ≤ 0.005). The mean total score of the Conners questionnaire before the surgery was 60.22 and decreased to 50.24, six months after the surgery (<i>P</i> &lt; 0.001). The McNemar analysis revealed a statistically significant reduction in clinically significant ADHD symptoms (T-score ≥ 65) following adenotonsillectomy (<i>χ²</i> = 10.46, <i>p</i> = 0.0012). The results indicated that in children with adenotonsillar hypertrophy, the surgery, in addition to improving arterial blood oxygen saturation, can solve their behavioral problems, significantly. Therefore, it is recommended to consider the tonsil size and respiratory status examination in children with cognitive or behavioral issues.</p>