Introduction: This study aimed to assess the capability of a pulse CO-oximeter to continuously monitor carboxyhemoglobin (COHb) during hyperbaric oxygen (HBO2) therapy. We estimated limits of agreement (LOA) between blood gas analysis and pulse CO-oximeter for COHb during HBO2 therapy in patients suffering from acute CO poisoning. Furthermore, we did a medicotechnical evaluation of the pulse CO-oximeter in hyperbaric conditions. Methods: We conducted a prospective, non-clinical, observational study in which we included n=10 patients with acute CO poisoning referred for HBO2 therapy. We did five repeated measurements of COHb for each patient during the HBO2 therapy. Bland-Altman analysis for multiple observations per individual was used to assess the agreement. The a priori LOA was ±6% for COHb. For the medicotechnical evaluation continuous measurements were obtained throughout each complete HBO2 therapy. The measurements were visually inspected and evaluated. Results: The Bland-Altman analysis showed that the pulse CO-oximeter overestimated COHb by 2.9 % [±1.0%] and the LOA was ±7.3% [±1.8%]. The continuous measurements by pulse CO-oximetry showed fluctuating levels of COHb and summarized saturations reached levels above 100%. Measurements were not affected by changes in pressure. Conclusion: To our knowledge, this study is the first to assess LOA and demonstrate use of a non-invasive method to measure COHb during HBO2 therapy. The pulse CO-oximeter performed within the manufactures reported LOA (±6%) despite hyperbaric conditions and was unaffected by changes in pressure. However, summarized saturations reached levels above 100%.