Research goals: retrospectively analyze the data of patients treated with hyperbaric oxygen in the Center for Underwater and Hyperbaric Medicine, Clinical Hospital Center Rijeka in the period from January 1 to December 31, 2017. The ultimate goal is to confirm the assumptions about the success of treatment with hyperbaric oxygen. Respondents and Methods: This study analyzes data obtained from the Integrated Hospital Information System (IBIS) and the documentation of the Center for Underwater and Hyperbaric Medicine of patients treated at the Center for Underwater and Hyperbaric Medicine, Clinical Hospital Center Rijeka, in the period from January 1 until December 31, 2017. The following data have been collected and analyzed: age and gender of the patient, indication for hyperbaric oxygen, duration of treatment (number of treatments) and outcome of treatment. The collected data are analyzed in Microsoft Excel and Statistica. During the research and data collection, ethical principles on secrecy of data by both individuals and institutions were respected. Results: Based on the outcome of treatment in 89% of patients, there was a clinical improvement, in 11% of patients no changes were noted, and in only 1 case, deterioration was reported. Conclusion: In this analysis, the initial presumption of the success of treatment with hyperbaric oxygen has been confirmed, but it also opened a new field for review and analysis that would show in more detail the effectiveness of hyperbaric oxygen treatment by type of diagnosis.