Background: Obstructive sleep apnea (OSA) in pediatric population is associated with cardiac, respiratory, metabolic, neurocognitive, and behavioral dysfunctions. Adenotonsillectomy (AT) is the treatment of choice in children who have hypertrophied adenoid and/or palatine tonsils. However, there is paucity of literature on the impact of AT on cardiorespiratory and sleep parameters in these cases. Methods: We did a retrospective study on children who had undergone AT from July 2016 to December 2018 at a tertiary hospital in north India. Only those children, whose polysomnography (PSG) was available both before and after AT were enrolled in this study. • Cardiac parameters: Mean heart rate (MHR) and highest heart rate (HHR), number and duration of arrhythmias, and pulse transit time (PTT) drops. • Respiratory parameters: Apnea-hypopnea index (AHI), respiratory disturbance index (RDI), oxygen desaturation index (ODI), mean oxygen saturation (MOS). • Sleep parameters: Time spent in different stages, sleep efficiency (SE), and arousal index (AI) on PSG were compared before and after AT. Results: A total of 56 children had undergone AT for OSA. Also, PSG, both before and after AT, was available in 37 children. After excluding children having undergone other surgeries for OSA and those with comorbidities, 32 children were enrolled. AT led to significant positive change in AHI (from 7.86 ± 7.91 to 2.03 ± 3.10, p = 0.01), RDI (from 16.319 ± 15.64 to 7.38 ± 3.72, p < 0.01), AI (from 22.10 ± 14.93 to 15.90 ± 8.48, p = 0.012), SE (from 91.47 ± 6.31 to 95.866 ± 3.03, p < 0.01), ODI (from 6.7959 ± 5.03 to 1.865 ± 2.09, p < 0.01), MOS (from 95.59 ± 2.19 to 97.28 ± 1.27), HHR (from 141.68 ± 17.93 to 120.93 ± 16.98, p < 0.01), MHR (86.68 ± 12.95 to 80.29 ± 8.81, p = 0.01), and PTT AI (from 36.67 ± 27.72 to 26.93 ± 24.86, p < 0.01). There was no non-sinus wide or narrow complex tachyarrhythmia in any child before or after AT. There was no statistically significant change in rapid eye movement (REM) sleep duration or number and duration of bradycardia episodes in these children (p > 0.05). Conclusion: Adenotonsillectomy improved SE and oxygenation, and decreased the number of obstructive events, arousals, heart rate, and PTT AI during sleep in children with OSA. Some children had residual disease after surgery. Heart rate and PTT can be excellent non-invasive parameters for detecting obstructive events during sleep in children and monitoring the impact of various therapeutic modalities.