Positive airway pressure (PAP) therapy is an effective treatment prescribed to children with sleep disordered breathing (SDB); however, PAP adherence remains challenging. Given that COVID-19 pandemic continues to impact sleep and daily life, the aim of this study was to evaluate longitudinal trajectory of PAP usage in children during the COVID-19 pandemic. Patients and Methods: This was a retrospective study. Children aged 1-18 years with SDB prescribed PAP at The Hospital for Sick Children (Toronto, Canada) were evaluated for PAP adherence. Demographics, medical history and PAP adherence data during four consecutive 3-month time periods from December 2019 to December 2020 were collected. These four time periods included i) prior to COVID-19 lockdown, ii) during the first three months of lockdown, iii) summer and iv) return to school period. Percentage of days where PAP was used for ≥4 hours and average nightly usage of PAP were primary outcomes. Results: A total of 149 children (61.7% male, mean (±SD) age=12.8 ± 4.1 years, BMI (±SD) z-score=1.45±1.43) were enrolled. Compared to prior to lockdown, the median (IQR) of percentage of PAP usage ≥4 hours and average nightly usage of PAP declined significantly during the summer and return to school periods (p<0.001 for all). By the end of the return to school period, only 69/149 (46%) showed sustained PAP usage and 80/149 (54%) had decreased PAP usage. Obesity was a risk factor for a decline in PAP usage after returning to school (β=−15.36, p=0.03). Conclusion: Compared to COVID-19 pre-pandemic PAP usage, there was a significant decline in PAP usage across COVID-19 pandemic. There is critical under usage of PAP in children diagnosed with SDB, resulting in an urgent need to address barriers to mitigate poor adherence to PAP long-term. Targeted strategies are required to optimize PAP adherence in children with SDB.