A 22 year-old-male-patient of Pyoderma Gangrenosum had been suffered from longstanding ulcers at his cheeks, nuchal region and upper back, which had been treated with corticosteroids and antibiotics without any effect. We have applied 49 times of hyperbaric oxygen therapy to the patient at 2.0~3.0 atmospheres absolute pressure. The pressure was increased for 15 min, then kept constant at the desired presseure for 30 min., and reduced to the atmospheric pressure within 5 min. The ulcer. had been treated with hyperbaric oxygen and revascularization was noted in the scars.