Objective To investigate the relationship between baseline snoring sound energy (SSE) and disease severity, changes in SSE after adenotonsillectomy, and the predictors of surgical success in children with obstructive sleep apnoea (OSA). Design Prospective cohort study. Setting Tertiary referral medical centre. Participants Thirty‐two children with OSA whose apnoea‐hypopnoea index ≥5 or apnoea‐hypopnoea index ≥1.5 with OSA comorbidities were recruited. Patients with complicated OSA were excluded. All participants underwent snoring sound analysis, polysomnography, and adenotonsillectomy. Main outcome measures Snoring sound energy and apnoea‐hypopnoea index were assessed at baseline and 6 months after adenotonsillectomy. Surgical success was defined as a postoperative apnoea‐hypopnoea index <1.5. Results The median age, body mass index, and apnoea‐hypopnoea index was 9 years, 19.0 kg/m2, and 13.2 events/h, respectively. Multivariate logistic regression showed that a baseline tonsil size of IV (odds ratio 15.7 [95% CI: 1.5‐166.3]) and SSE of 801‐1000 Hz > 21.9 dB (odds ratio 32.3 [95% CI: 2.6‐396.6]) were significantly related to severe OSA. Following adenotonsillectomy, apnoea‐hypopnoea index decreased significantly (P < 0.001). SSE of 41‐200 Hz, 201‐400 Hz and 801‐1000 Hz also decreased significantly (P = 0.04, 0.01 and 0.006, respectively). Baseline SSE of 801‐1000 Hz < 8.5 dB significantly predicted surgical success (odds ratio 11.0 [95% CI: 1.4‐85.2]). Conclusions Our findings suggest the potential utility of SSE of 801‐1000 Hz to screen for severe OSA, predict surgical success and assess therapeutic outcomes. Specific baseline SSE may represent a potential biomarker for childhood OSA.