Hyperbaric oxygen therapy (HBOT) is highly safe in treatments based on internationally accepted treatment tables. However, in some long-term treatments, the internal adjuvant and the patient are exposed to some toxic effects. Oxygen shows toxic effects when inhaled in a high-pressure environment for long periods or above partial pressures of 3 ATA. The excess oxygen has a toxic effect on the lung and central nervous system. Oxygen poisoning can be seen in long-term oxygen therapy in intensive care, in closed or semi-closed circuit diving, in saturation dives, on decompressions on the surface, in recompression, and HBOT.