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Introduction Positive pressure remains the main treatment for obstructive sleep apnea (OSA). Compared to traditional continuous positive airway pressure (CPAP) machines with fixed pressure settings, AutoCPAP machines can titrate settings based on user requirements and transmit data to the pulmonologist. While bariatric surgery has been associated with improvement in OSA, there is little data examining associations between postoperative weight loss and positive pressure requirements longitudinally. The purpose of this study was to evaluate changes in AutoCPAP pressure settings as a function of weight loss over time. Methods A retrospective review of bariatric surgery patients at a single institution from 2018-2022 was performed. Participants included patients with OSA who used an AutoCPAP machine and had at least one appointment within the first 18 months postoperatively. Preoperative BMI, postoperative BMI and percent excess weight loss were analyzed. AutoCPAP parameters used as markers of OSA severity included 95th or 90th percentile pressure depending on the machine and apnea-hypopnea index (AHI). Paired t-tests were performed to evaluate changes in BMI and 90th/95th percentile pressures. Linear regressions with fixed effects were performed to investigate changes in pressures and BMI over time. Results 345 patients with OSA who underwent bariatric surgery and were prescribed AutoCPAP were evaluated. Of those, twenty-eight (8%) were compliant with their AutoCPAP and were included in this study. Overall, 90th/95th percentile pressures improved postoperatively by 1.32 cmH2O± 0.33 (P= 0.003). Patients with a preoperative BMI ≥40 demonstrated improved 90th/95th percentile pressures over time by 1.22 cmH2O± 0.34 (P=0.002) while those with a preoperative BMI < 40 did not (-1.7 cmH2O ± 0.86; P= 0.106). Reduction in BMI was associated with reduction in 90th/95th percentile pressures at 2-6 weeks and 2-6 months postoperatively. Conclusion Patients with a higher preoperative BMI demonstrated improved positive pressure requirements postoperatively compared to patients with a lower preoperative BMI. This suggests that there may be a critical BMI after which further weight loss is not associated with significant improvements in OSA. Further, positive pressure requirements may decrease most significantly within the first several months postoperatively. Support (if any)