The article presents a case study of a 32-year-old patient admitted to the Mazowia Hyperbaric Therapy Centre due to a sudden loss of hearing. In an interview the patient reported an abrupt hearing deterioration in his right ear and the feeling of congestion in the left ear with bilateral tinnitus present for over 2 months. The patient was qualified to undergo hyperbaric oxygen therapy (HBO). After 15 treatment sessions in a pressure chamber a noticeable improvement of hearing in his right-ear was noted (proved by pure tone audiometry) and subjective hearing upswing in his left ear. The bibliography includes the articles and references concerning the time limits of HBO therapy and its effectiveness in the treatment of sudden deafness.