A single session of hyperbaric oxygen therapy (HBO2T) is known to act on the parasympathetic system and also increase the production of reactive oxygen species. However, the impact of a treatment series consisting of 20 to 40 sessions on blood pressure (BP) remains unknown. Thus, the current study aimed to assess the effect of this type of treatment in patients administered HBO2T as an adjunct therapy for wound healing. We retrospectively analyzed data from 93 patients treated for wound healing. All patients were treated in the Perry Sigma Plus DuoPlace hyperbaric chamber at the CSSS Alphonse Desjardins Centre Hospitalier Affilié Universitaire/CHAU de Lévis (Québec, Canada) between 2003 and 2010. They were exposed daily to 100% oxygen at 2.5 atmospheres absolute (atm abs) for 90 minutes. The systolic BP (SBP), diastolic BP (DBP) and heart rate (HR) were measured before each HBO2T session, and patient age and sex were also recorded. The impact of HBO2T on BP was evaluated using linear mixed models. The mean age of the patients was 66.6 years (standard deviation: 10.8). The majority of the subjects was male (79.6%) and suffered from Type 2 diabetes (71.9%) and hypertension (65.6%). These patients received an average of 25 HBO2T sessions. Before the first treatment, the mean SBP and DBP measurements were 145 (24.8) mmHg and 78 (13.1) mmHg, respectively; the median recorded HR was 69.0 beats/minute (interquartile range: 63.0-81.5). The age- and sex-adjusted mixed models revealed that HBO2T was significantly associated with a decrease in the HR and SBP measurements; the greatest impact was observed during the first 20 treatments for HR (p-value < 0.5) and the last 20 treatments for SBP (p-value < 0.0001). No effects of HBO2T on DBP were detected (p-value = 0.36). In patients with chronic wounds requiring HBO2T, successive HBO2T treatments affect HR and SBP measurements. However, further prospective clinical investigations are required to evaluate the prolonged effects of HBO2T. Chateau-Degat, Belley, , , , , , , (). Hyperbaric oxygen therapy decreases blood pressure in patients with chronic wounds. Undersea & hyperbaric medicine : journal of the Undersea and Hyperbaric Medical Society, Inc, ;39(5):881-9. https://www.ncbi.nlm.nih.gov/pubmed/23045916